We report on a child with Klinefelter syndrome and short stature due to idiopathic growth hormone deficiency (IGHD). His height was below the mid-parental height, with a significant delay in bone age. Height velocity increased from 4.5 to 8.2 cm/year during 1 year of GH therapy and typical catch-up growth was observed. No adverse reactions to the treatment were observed. We wish to emphasize the rare association between Klinefelter syndrome and IGHD and the apparent effectiveness and safety of recombinant somatotropin treatment in aneuploid patients. © 1994 Wiley-Liss, Inc.