Rectal prolapse occurs most commonly in children and middle-aged and elderly women and is relatively rare in young men and is occasionally caused by bladder stones. Severe rectal prolapse, bilateral hydronephrosis, and renal insufficiency caused by bladder stones are rare in a 30-year-old man. We report the case of a 30-year-old male patient with cerebral palsy who presented with a large bladder stone that resulted in severe rectal prolapse, bilateral hydronephrosis, and renal insufficiency. Following a definitive diagnosis, the bladder stone was successfully removed, and his kidney function returned to normal. We assessed the patient's nutritional status and stone composition and concluded that the main cause was malnutrition. Rectal prolapse is a rare clinical manifestation of bladder stones, particularly in young adults. Cerebral palsy patients are a vulnerable group in society because of their intellectual disabilities and communicative impairments. Accordingly, besides taking care of their daily diet, abnormal signs in their bodies should receive the doctors' attention in a timely manner.