Rectal foreign body impaction in infancy is extremely rare, and the literature does not describe a standard treatment procedure. Extraction by fiberoptic rectosigmoidoscope is advocated as the treatment of choice but is not free of possible complications. It should be also taken into consideration that the type of foreign body has an impact on the timing of treatment. We report a 50-day-old male presenting with a retained broken tip of a mercury thermometer in the rectum. A novel method of diagnostic approach and treatment is discussed.