A case of horseshoe kidney is reported in a 11 week-old fetus affected by trisomy 18. Macroscopic examination did not show any other pathological change. The histological picture of the fused-kidney was characterized by architectural and glomerular changes. At x 100 magnification, large areas of metanephric mesenchyme, characterized by spindle cells surrounded by a loose oedematous stroma, were detected in the deep cortex and in the medulla. At higher power, multiple glomerular changes were observed. Maldeveloped glomeruli showed enlarged capsular spaces, adhesions between vascular tuft and capsular cells, podocytes in multiple layers, and large glomerular bodies formed by two vascular tufts. Our data confirm previous reports on glomerular changes in horseshoe kidney, and reinforce the hypothesis that horseshoe kidney should not be considered a simple fusion problem, but a complex developmental abnormality, possibly involving glomerular development.