The cases of 52 patients with Propionibacterium acnes infection of orthopaedic implants are summarized: 20 patients with definite infection (sepsis, with P. acnes recovered from multiple specimens per patient), 15 with probable infection (sepsis, with P. acnes recovered from one specimen), and 17 with possible infection (signs of prosthetic malfunction or pseudo-osteoarthritis, with P. acnes recovered from one specimen). The patient population consisted of 37 males and 15 females with a mean age of 51.8 years (range 17-88). Besides bone surgery, 21% of these patients had severe coexisting illness. The study population was very heterogeneous and clinical presentation very polymorphic; infections became clinically apparent through sepsis, prosthetic malfunction, or a delay in consolidation. The diagnosis was highly dependent on the quality of the samples taken and the methodology used by the microbiology laboratory to isolate this bacterium. Culture time was long, on average 11.4 days. Treatment involved a combination of antibiotic treatments (67% of cases) and ablation of the material (83% of cases). Although P. acnes is considered to be weakly pathogenic, this bacterium may be responsible for infections in patients with implanted orthopaedic material. Ablation of the arthroplastic or osteosynthetic material is necessary in the majority of cases.