Prolonged potent topical glucocorticoid therapy in infants can cause iatrogenic Cushing's syndrome. This case highlights the rarity of poor weight gain in iatrogenic Cushing's syndrome. A 17-month-old boy was referred to outpatients pediatric endocrine clinic for evaluation of growth failure. On presentation his weight was 9.7 kg (5th percentile) and height was 72 cm (-3.6 SD below mean for age and sex). Systemic examination revealed grossly moon-like face, hypertrichosis and thin skin in the genital area. His mother reported using local clobetasol for the previous seven months for his diaper dermatitis. Baseline plasma cortisol was low (0.3 ng/ml, normal range: 60 to 280 ng/ml). During standard dose of synthetic adrenocorticotropic hormone test, the peak cortisol level was 0.4 ng/ml (N >180 ng/ml) and was consistent with hypothalamic–pituitary–adrenal axis suppression. The patient's clinical presentation and laboratory investigations confirmed the diagnosis of secondary adrenal insufficiency and iatrogenic Cushing's syndrome. He was treated successfully by discontinuing use of clobetasol. His appearance and growth returned to normal within two months. Morning cortisol was 101.2 ng/ml after stopping the oral physiologic dose of hydrocortisone. Our case differed from other reports of iatrogenic Cushing's syndrome by presenting in poor weight gain rather than obesity.