Introduction. Peri-prosthetic infections due to P. acnes may present as Prosthesis dysfunction without any obvious sepsis. We present our experience of efficient management of total knee prosthesis infection secondary to P. acnes which is one of the biggest case series. Materials and methods. From 2008 to 2009, 9 patients diagnosed with P. acnes infection after knee arthroplasty were retrospectively reviewed and analysed for clinical diagnosis; laboratory data (ESR, CRP); Radiological Imaging; number of days for culture growth of P acnes; organism sensitivities; antibiotic regimen and length of treatment and surgical management. Infection was diagnosed by 2 positive cultures. Results. Group 1 had 6 patients with confirmed knee prosthetic infection. 4 patients had no P.acnes detected from knee aspiration samples. All underwent two stage revisions. Group 2 had 3 patients with prosthesis dysfunction and pain without any obvious infection. All patients underwent frozen section histology test. Depending on results 2 patients with positive result had two stage revision surgeries and 1 patient with negative result had Single stage surgery. Antibiotics were administered for variable duration (4-10 weeks). In group 1 the average initial ESR and CRP were 45 mm/h and 28 mg/dl, respectively. 1. In group 2 average ESR was 15 and CRP was 6. The average number of days for positive culture was 6. All cultures were sensitive to Penicillin G and Vancomycin. All patients were treated successfully except one patient from group 1 who needed knee arthrodesis while one patient from group 2 received long term suppressive therapy. Discussion. P. acnes can cause peri-prosthetic infection where classical signs of sepsis are absent and therefore should be suspected in patients who present with subtle, delayed symptoms following joint arthroplasty. Many laboratories discard culture samples after 5 days. In our series the average time period for positive P. acnes culture is 6 days (range 5-10 days). The cultures may not be positive for as long as 10 days. So it is very important to keep the cultures for at least two weeks before discarding