Ring chromosome 15 syndrome is a rare condition in which severe growth retardation is a major finding. We report a 4 year old boy with the karyotype 46,XY, r(15)(p11.2q26.2) whom we have treated with recombinant human growth hormone (GH) for two years. During the first year of treatment, the insulin-like growth factor I increased from subnormal 4.2 nmol/l to normal 13.8 nmol/l and the insulin-like growth factor binding protein 3 levels increased from 2.6 to 3.8 mg/l, whereas high binding protein 1 concentrations normalised from 52.0 to 16.7 micrograms/l. During the two years of treatment his relative height improved from -6.2 SD to -4.4 SD and the predicted adult height from 159.6 cm to 163.5 cm. Owing to the good growth response, we have decided to continue GH treatment.