Annular pustular psoriasis (APP) is a rare form of pustular psoriasis with a chronic relapsing course and a good prognosis. The clinical picture is characterized by erythematous lesions, usually polycyclic, with the presence of small, sterile pustules on the circumference of the lesions and fine peeling. We present two cases of APP with diagnostic problems: a 65-year-old woman that suffered from intermittent APP with remission and exacerbation for many years, and an 83-year-old man with lesions that developed after atenolol treatment. In both cases, the patients were thought to have drug provocation, and therefore acute generalized exanthematous pustulosis (AGEP) was diagnosed. Only a thorough analysis of the course of the disease and histopathological examination allowed correct diagnosis. The clinical picture of APP is similar to AGEP, generalized pustular psoriasis (GPP), also known as von Zumbusch pustular psoriasis, and subcorneal pustular disease, and it requires accurate differential diagnosis.