Aggressive fibromatosis or desmoid tumor, is a histologically benign entity with unknown etiology that may present a serious clinical course. Due to its high tendency to recur and local aggressive behavior and as there is no established effective medical treatment, complete surgical excision remains the sole management. To our knowledge, we describe the first case of giant desmoid tumor which arised from ileal neobladder mesenterium in a bladder cancer patient with orthotopic substitution.