In 1969-1973, acute yersiniosis was diagnosed in 30 cases of erythema nodosum (EN), in 6 cases of EN and simultaneous erythema multiforme (EM), in 1 case of EN and erythema figuratum, in 1 case of EM, and in 1 case of drug eruption-like exanthema. During these years, 180 patients with EN due to other causes were seen. The most marked difference in the clinical course between yersiniosis and other cases was the duration of the eruption. EN nodules in Yersinia EN faded away in 4 wk in all but 1 case while the 4-wk cure rate among the other patients with EN was only 37%. There were 2 types of EM lesions, namely cockade-like lesions and vesicopapules. They usually appeared some days before or together with EN nodules and they disappeared within 2 weeks without any scarring. Yersiniosis was caused by Y. enterocolitica serotype 3 in 19 cases, Y. enterocolitica serotype 9 in 17 cases, and Y. pseudotuberculosis in 3 cases. Of the patients, 21 suffered from abdominal pains and/or diarrhea prior to skin manifestations; 11 had no preceding symptoms; 8 of the other 180 patients with EN had gastrointestinal symptoms resembling those of yersiniosis.