An outbreak of shigellosis is described in an intermediate care hospital for children, where routine isolation procedures failed to halt the outbreak. Two weeks after the appearance of the first case, small numbers of patients became symptomatic with fever and diarrhea, but remained culture-negative. One week later, two patients with positive cultures were identified, with many other symptomatic patients having negative cultures. Twenty-five days after identification of the first case, there were fourteen cases identified with shigellosis and many more symptomatic patients. It was at that time that hospital-wide measures of infection control were instituted, and treatment of all patients, infected and uninfected, was initiated with trimethoprim-sulfamethoxazole (TMP-SMX). No new cases of shigellosis were diagnosed after initiation of treatment, and symptoms abated within 72 hours.