© 2017 by Turkish Pediatric Endocrinology and Diabetes Society.Rabson-Mendenhall syndrome (RMS) is an autosomal recessive disorder due to mutations in the insulin receptor gene (INSR) which is mapped to 19p13.2. RMS is characterized by acanthosis nigricans, generalized lanugo, tooth and nail dysplasia, high nasal bridge, and growth retardation. A 5-year-old female patient was referred due to acanthosis nigricans and generalized lanugo. On her physical examination, severe acanthosis nigricans of the neck, axillae, the external genitalia and antecubital regions, generalized lanugo, mildly decreased subcutaneous fat, dysmorphic facial features, and polydactyly on her left hand were noted. Insulin resistance and impaired glucose tolerance were found. Sequence analysis of the INSR in the patient revealed c.3529+5G>A mutation in homozygous state. RMS should be suspected in a patient with characteristic physical features and insulin resistance.