An epidemic of 135 cases of chancroid occurred in Winnipeg, Manitoba, Canada, from July 1975 to September 1977. Probable contributing factors for development of chancroid lesions included male sex, lack of circumcision, and genital trauma. A previous history of venereal disease, sexual contact with a person from a bar or hotel in the core city area, unemployment, alcoholism, American Indian or Métis (mixed American Indian and Caucasian) race, and unstable domestic relationships were often accessory findings for infected patients. The tracing and treatment of lesion-free contacts of patients with chancroid may have contributed to the restriction of the outbreak to the core city area. Nineteen isolations of Hemophilus ducreyi were made, most by the use of a new selective medium. Treatment with a short course of penicillin antibiotics was ineffective for 10 of 16 patients, whereas an adequate course of sulfonamide or tetracycline antibiotics, combined when necessary with drainage of fluctuant inguinal abscesses, was effective therapy for most patients.