Hemihypertrophy is a clinical condition defined as an asymmetric enlargement of one side of the body. Inguinal hernias, renal cysts, cryptorchidism, ectasias of collecting tubes, medullary sponge kidney and horse-shoe kidney are examples of abnormalities associated with hemihypertrophy that have been described in the literature. We report here a 17.2-year-old patient with a left hemihypertrophy and renal agenesis with contralateral right compensatory renal hypertrophy together with normal renal function and blood pressure in the absence of proteinuria. He also presented with faint macular hyperpigmented skin lesions on his left upper arm, forehead and abdomen. To the best of our knowledge, this is the first report of renal agenesis and hemihypertrophy in the same patient. Hemihypertrophy can be seen as a component of Klippel-Trenaunay-Weber syndrome. The other components of this syndrome are varicose veins, skin naevus and arteriovenous malformations. Although renal agenesis, hemihypertrophy and hyperpigmented macular skin lesions (skin naevuses) may be incidental findings, together they may form a variant of Klippel-Trenaunay-Weber syndrome, as in our case.