This article describes an unexpected case of a giant neobladder stone in a female that was diagnosed incidentally for a concurrent ovarian disease, without clinical or instrumental evidence of neobladder over distension. In July 1989, M.A., woman, 39-years old, underwent radical cystectomy, saving the uterus and the ovaries, and orthotopic ileal bladder substitution. Twelve years later she had symptoms of diffuse abdominal discomfort for about one month, without noticeable urinary symptoms or urinary retention. Enhanced CT and a subsequent MRI showed the presence of a 10 x 12.5 x 19 cm capsulated ovaric mass with sharp edges and associated obstructive bilateral hydroureteronephrosis, and an oval-shaped stone with a 10 cm longitudinal diameter, which occupied the majority of the neobladder cavity. The patient underwent surgical operation to remove the ovaric mass (fibrotecoma) and to extract the giant floating stone by a neocystotomy. Its dimensions were 10.5 x 7 x 7 cm, weighing 760 g. The stone was triple phosphate on chemical-physical analysis. The case reveals that neobladder stones can be associated with very few symptoms and if an appropriate follow-up is not performed they can become of remarkable dimensions.