We provide a molecular and pathophysiological characterization of an 11-year-old male patient, with a diagnosis of renal hypodysplasia, cysts and chronic renal failure. Although previously normoglycaemic and with a negative familial history for diabetes mellitus, he developed fasting hyperglycaemia within 12 months of the start of treatment with recombinant human growth hormone (rhGH). Direct sequencing of the HNF1 beta gene revealed a de novo heterozygous mutation in exon 2, c.535delC [Pro118LeuX7]+[=]. The appearance of fasting hyperglycaemia following rhGH treatment in children with renal cystic hypodysplasia suggests that investigation of the HNF1 beta gene is warranted, even when familial history is negative for diabetes. This is particularly important in regard to genetic counselling.