OBJECTIVE: To identify and validate previously established phenotypes of knee osteoarthritis (OA) based on similarities in clinical patient characteristics. METHODS: Knee OA patients (N = 551) from the Amsterdam OA (AMS-OA) cohort provided data. Four clinical patient characteristics were assessed: upper leg muscle strength, body mass index (BMI), radiographic severity (Kellgren/Lawrence [KL] grade), and depressive mood (the Hospital Anxiety and Depression Scale [HADS] questionnaire). Cluster analysis was performed to identify the optimal number of phenotypes. Differences in clinical characteristics between the phenotypes were analyzed with ANOVA. RESULTS: Cluster analysis identified five phenotypes of knee OA patients: "minimal joint disease phenotype", "strong muscle strength phenotype", "severe radiographic OA phenotype", "obese phenotype", and "depressive mood phenotype". CONCLUSIONS: Among patients with knee OA, five phenotypes were identified based on four clinical characteristics. To a high degree, the results are a replication of earlier findings in the OA Initiative, indicating that these five phenotypes seem a stable, valid, and clinically relevant finding.