Objective: Testicular adrenal rest tumours (TART) are a well-known complication in adult male patients with congenital adrenal hyperplasia (CAH), with a reported prevalence of up to 94%. In adulthood, the tumours are associated with gonadal dysfunction most probably due to longstanding obstruction of the seminiferous tubules. The aim of our study was to determine the presence of TART and their influence on gonadal function in childhood. Design: Retrospective study. Patients and methods: Scrotal ultrasound was performed in 34 children with CAH due to 21-hydroxylase deficiency who were between 2 and 18 years old. FSH, LH, testosterone and inhibin B concentrations were measured in serum of 27 patients. Results: TART were detected by ultrasound in 8 out of 34 (24%) children. In two of them, bilateral tumours were found. All lesions were located in the rete testis. Seven patients had the salt-wasting type of CAH; one patient had the simple virilising type of CAH. Mean tumour size was 4.1 mm (range 2–8 mm). In none of the patients were the tumours palpable. Two children with TART were between 5 and 10 years old, the other six children were above 10 years old. In all children with TART, LH, FSH, testosterone and inhibin B levels were similar to the patients without TART. Conclusion: TART can be found in CAH children before the age of 10 years. The absence of gonadal dysfunction in our group of children suggests that gonadal dysfunction as frequently reported in adult CAH patients with TART develops after childhood.