The term primary chronic osteomyelitis covers a heterogeneous spectrum of clinical features that should be separated for therapeutic reasons. Unifocal manifestations should be distinguished from multifocal ones. While bacteria are often found in the first group, bacteriological investigations are usually negative in the second group. Additionally, multifocal forms often recur (chronic multifocal recurrent osteomyelitis), possess a long clinical course and may be combined with dermatological disorders (SAPHO syndrome). A biopsy is often necessary for tumor exclusion and obtaining material for bacteriology. Histology cannot differentiate between the respective forms of chronic osteomyelitis.