Abstract: Aim: To evaluate effectiveness of arthroscopic drainage of acute septic arthritis knee in adult population. Materials and method: 19 patients with average age of 38.9 years (19-66 years) evaluated retrospectively and prospectively, for a minimum follow-up period of 6 months (6-28 months), on Tegner-Lysholm Knee Scoring Scale. Arthroscopic drainage was performed on these patients at an average delay of 6.84 (4-17) days after onset of symptoms, followed by immediate intravenous antibiotics and then oral therapy, as per culture-sensitivity, with active physiotherapy. Repeat arthroscopic lavage was performed where required. Results: 16 of 19 patients (84.2%) had good or excellent results, while 3 had fair results, of which 2 had recurrence of acute septic arthritis and 1 progressed to chronic osteomyelitis of tibia. Successful elimination of infection seen in 94.7%. Conclusion: Arthroscopic drainage is safe and effective alternative to the gold standard procedure of open arthrotomy and debridement for acute septic arthritis knee in adult population. Early debridement and lesser Gachter stage more often lead to good to excellent results.