OBJECTIVE: The Cohort Hip and Cohort Knee (CHECK) is a cohort of middle-aged individuals with hip or knee pain. Radiographs were assigned Kellgren & Lawrence (KL) scores under different conditions at each follow-up visit for 10 years. We aimed to describe and consolidate each scoring approach, then illustrate implications of their use by comparing baseline KL scores assigned using two of these approaches, and evaluating their respective associations with joint replacement and incident radiographic osteoarthritis (ROA). METHODS: We compared baseline KL scores assigned to hips and knees using two scoring approaches: (i) assigned by senior researchers to baseline images alone, and (ii) assigned by trained readers, read paired and in known sequence with up to 10 years of follow-up radiographs (Poisson regression). We evaluated the associations of baseline ROA (any ≥ KL1, established ≥ KL2) with joint replacement, and of KL1 joints with incident established ROA (survival analysis). RESULTS: Of 1002 participants (79% women, mean (SD) age 55.9 (5.2) years, BMI 26.2 (4.0) kg/m2 ), the second scoring approach had 2.4 (95% CI 1.8-3.1, knees) and 2.9 (2.3-3.7, hips) times higher prevalence of established ROA than the first approach. Established hip ROA had higher risk of joint replacement using the first approach (Hazard Ratio, HR 24.2 (95%CI 15.0-39.8) vs. 7.7 (4.9-12.1), second approach), as did knees (19.3 (10.3-36.1) vs. 4.8 (2.4-9.6)). Risk of incident ROA did not differ by approach. CONCLUSIONS: This study demonstrates that evaluating ROA prevalence and predicting outcomes depends on scoring approach.