An epidemic of respiratory tract diphtheria began in Russia in 1989. In 1994 more than 2,500 cases occurred in St. Petersburg alone. We describe clinical findings in the 1,860 adult patients treated in Botkin's Hospital. The study is based on a retrospective review of patient records. In 98% of the patients the diagnosis was confirmed by a positive throat culture growing a toxin producing strain of Corynebacterium diphtheriae. A catarrhal disease without membranes was present in 1,256 (67.5%) patients, 150 patients had membranes on tonsils only, 268 patients on tonsils, the uvula, soft palate and posterior pharynx and 35 patients on larynx or in the lower respiratory tract. 42 patients (2.3%) died. Among the deceased patients 26 were alcoholics, whereby the death rate for non-alcoholics was probably around 1%. 151 patients (8.1%) had a toxic form of the disease with swelling of the neck. This form of the disease carried a high mortality, 25.7%. In a subgroup of 1,045 patients the protective efficacy of vaccination could be evaluated. A 2.2-fold protection was found, but the study may underestimate the efficacy. We conclude, that if a wide diphtheria epidemic affects an industrialized country, it would probably not any more be the big killer that it was in Europe and in the United States in the 1950's and 1960's.