Jack Murray Costello was born in Gisborne to Herbert Costello, a businessman, and Ethna Costello (nee Prince.) During his childhood, the family moved to the Thames coast where Jack attended Thames High School, and was Dux of that school in 1947.

In 1948, Jack enrolled in the Auckland University College Medical Intermediate course, and was subsequently accepted into the second year of the Medical Course in Dunedin in 1950. In 1954, he was capped with Distinction in Medicine and awarded the Colquhoun Memorial Medal and Prize, and the Marjorie McCallum Medal. This was no surprise to his contemporaries and teachers as his devotion to excellence was apparent to all. After graduation he worked in resident positions in the Waikato Hospital, and spent three months in general practice in Tokanui Special Area, Southland, New Zealand. He often recalled the extraordinary experiences he had in this remote practice.

Thereafter, he became a Medical Registrar at the Dunedin Hospital before departing for London as a ship's surgeon. There he took up a training position in the Queen Elizabeth Hospital for Children in 1959, and continued with training for his vocation in paediatrics as a Registrar at the University College Hospital London. These were classical moves at the time to become established as a paediatrician.

He returned to Auckland in 1963, as a Junior Paediatric Specialist at the Princess Mary Hospital for Children. From 1965 onward, he was Paediatrician at this hospital and also the neonatal wards of National Women's Hospital, the latter from 1965 to 1970. During this time he established a paediatric presence at the Growth and Development Clinic, which continued through to 1992.

Thus far Jack's career had developed as a clinician, but in 1970, he took up the post of Senior Lecturer in the Department of Paediatrics in the new School of Medicine in Auckland. His clinical training and expertise now came into play as a teacher. A whole generation of undergraduates and graduates benefited from his inimitable skills, and these were also recognised by his peers as signified by his ever increasing membership of specialist committees such as the Clinical Subcommittee of the National Growth Hormone Committee of the Medical Research Council (1976 to 1989), President of the Auckland Clinical Society (1970) Chairman Auckland Branch Paediatric Society of New Zealand (1972 to 1977), Supervisor of Basic Physician Training in Paediatrics (a Royal Australasian College of Physicians appointment) in the 1970s, Chairman, Paediatric Advisory Committee on postgraduate training in the University of Auckland in the 1970s, to name but a few of many such positions, all of which indicated recognition of his immense erudition in matters paediatric.

He was appointed Associate Professor in Paediatrics, and continued his clinical and teaching duties at the Princess Mary Hospital until the last few years before his retirement, when he helped establish a paediatric ward in Middlemore Hospital.

He had 13 publications in peer reviewed scientific journals. These related to matters usually reflecting meticulous and painstaking clinical observation. The publication he will be remembered for most concerns a rare congenital anomaly which bears his name, the Costello Syndrome, as he was the first to recognise and document it. There is an international Costello Syndrome Society which consists of families afflicted by this disease.

This is a summary of Jack's active career as a doctor. It does not give justice to his clinical and teaching skills. Jack was a paediatrician's paediatrician, to whom all turned when their children were sick. They did so because they all recognised in Jack, a man who would be indefatigable in the pursuit of an accurate diagnosis and the best of treatment. His clinical skills were legendary. His students were in awe of his dedication to doing his absolute best at all times. By personal example he demonstrated excellence in clinical practice.

Jack was a quiet, kindly and mostly gentle person. The exception to the latter was if he perceived that someone was not doing their best for sick children, when he could become quite fierce. He was a champion of the new Children's Hospital in Auckland. Some felt it should have been named after him.

His hobbies were those of a family man; gardening, walking, furniture renovation. He and Barbara, his wife since 1960, enjoyed dancing. He is survived by his two children, Grant and Debbie, and his two grandchildren, Grace and Thomas.