We report a case of giant renal calculus of 14 × 10.5 × 9 cm in size and weighing 790 g, in a horseshoe kidney, along with two large calculi on the opposite side. Patient presented with unusual complaint of an abdominal lump only. Physical examination revealed a stony hard mass on the left side of the abdomen, extending from the subcostal region to just above the iliac crest. A giant renal calculus on the left and two large calculi on the right side of a horseshoe kidney were diagnosed on computed tomography (CT) scan. Percutaneous nephrolithotomy, followed after 5 days by open pyelolithotomy was done for the stones on the right and left side, respectively. Analysis revealed a calcium phosphate stone. This case is worth reporting as it was not only the 8th heaviest renal stone reported in the English literature, but also the first giant stone to be reported in a horseshoe kidney.