Low-grade infection was systematically searched for in all revision shoulder surgeries by harvesting tissue samples. Ten consecutive patients were identified with a non-purulent low-grade infection of the shoulder. All of these patients suffered from pain and eight were stiff. Preoperative aspiration in eight patients yielded bacterial growth in only one case. Serum C-reactive protein levels were normal in seven out of 10 cases. Propionibacterium acnes was identified in seven, coagulase-negative Staphylococcus in two and Staphylococcus saccharolyticus in one case. The delay between harvesting the tissue samples and detection of bacterial growth averaged eight days (range, 2-17). After debridement and antibiotic treatment for a mean of 4.5 months, tissue samples were repeatedly harvested in nine patients due to persistent pain. The infection was microbiologically eradicated in six out of nine cases that had a repeated biopsy. However, nine out of 10 patients continued to suffer from moderate to severe pain. Low-grade infection of the shoulder can be a cause of persistent pain and stiffness. The results of antibiotic treatment are disappointing. Further studies are necessary to analyse this difficult pathology.