BACKGROUND Stiff knees are defined as those with an arc of motion < 50°. They pose a considerable surgical challenge to the operating surgeon. Based on our experience to deal with these complex cases, we have developed a working classification that outlines a flowchart to manage the stiff/ankylosed knees. METHODS It was a retrospective study conducted in our department. Out of 570 TKA performed in last 5 years, 57 had stiffness and four had bony ankyloses (total 61 knees). Patients were classified based on the fibrous or bony ankylosis and preoperative ROM. RESULTS Patients were followed for an average 2.4 years (1.8-5.5 years). KSS pain scores improved from an av. 32 preop (18-64) to av. 76 postoperatively (61-90). The KSS function scores improved from a preoperative value of 36 (16-56) to an av. 78 (52-90) postoperatively. ROM improved from an average of 35.6° (0°-44°) preoperatively to an average of 95.6° (ROM 73°-118°) postoperatively. Extension lag was an av. 8° (3°-12°) and was seen in 13 patients postoperatively. Residual fixed flexion deformity was an av. 7° (3°-14°) and seen in 17 patients. The stiff knees (type 1 and type 2) fared better than ankylosed knees (type 3) in all aspects. Complication rate was high (24%) in our series. CONCLUSIONS Our classification of stiff/ankylosed knees guides the surgeon to decide upon which approach to take, which implants to keep handy and has a predictive and prognostic value.