BACKGROUND AND PURPOSE: The concept of fast-track surgery has led to a decline in length of stay after total hip arthroplasty (THA) and total knee arthroplasty (TKA) to about 2-4 days. However, it has been questioned whether this is only achievable in selected patients-or in all patients. We therefore investigated the role of preoperative pain and functional characteristics in discharge readiness and actual LOS in fast-track THA and TKA. METHODS: Before surgery, hip pain (THA) or knee pain (TKA), lower-extremity muscle power, functional performance, and physical activity were assessed in a sample of 153 [corrected] patients and used as independent variables to predict the outcome (dependent variable) – readiness for hospital discharge – for each type of surgery. Discharge readiness was assessed twice daily by blinded assessors RESULTS: Median discharge readiness and actual length of stay until discharge were both 2 days. Univariate linear regression followed by multiple linear regression revealed that age was the only independent predictor of discharge readiness in THA and TKA, but the standardized coefficients were small (≤ 0.03). INTERPRETATION: These results support the idea that fast-track THA and TKA with a length of stay of about 2-4 days can be achieved for most patients independently of preoperative functional characteristics.