Between August 1974 and October 1975 78 patients with mycoplasma-pneumonia-infection were admitted to the 3 pediatric clinics of Hannover. Their clinical and radiological findings were studied. 20 patients with serological diagnosis of additional viral infection were not included in this study. The clinical diagnosis was confirmed by complement fixation test. The commonest symptoms were fever, coughing and abnormal auscultatory findings over the lungs. Chest roentgenograms showed three different patterns of infiltration: 1. Disseminated, non homogenous bronchial lines and mottled shadows often with swollen hilar lymphnodes in 46% of all patients.--2. Homogenous, extensive, opaque infiltrates in 29% of all patients.--3. Perivascular and peribronchial infiltrates at the hilus with or without swollen lymphnodes in 21% of all patients.--This means that in half of the patients abnormal signs in chestroentgenogram (type 2 and 3) were present, which formerly were described as "atypical pneumonia."--4. There were no radiological symptoms in 4% of the patients.--Those who were treated with tetracyclin or erythromycin became afebrile within 1--3 days, in those who didn't get antibiotics at all or were treated with other antibiotics fever lasted longer.