The aim of this study was to describe the range and cost of investigations ordered by paediatricians for children with mild to moderate developmental delay. A total of 79 consultants on the Thames Regions Consultant Community Paediatricians database were sent a faxed questionnaire and 86% of the paediatricians responded. The number of tests ordered by each paediatrician ranged from none to 15; 26 different medical investigations were selected. The four most common tests were chromosomes for karyotyping, fragile X testing, thyroid function testing and metabolic studies which each appeared in over half of the responses. The median cost of the investigations chosen was 386 Pounds with a range from 0-1181 Pounds. This study revealed marked variations in clinical practice when paediatricians investigate a developmentally delayed child. This was found to reflect both personal bias and a lack of consensus in the medical literature. There is a need for accurate community based prevalence data on causes of developmental delay, and critical appraisal of the available diagnostic tests.