['The authors investigated whether deletion of chromosome 9p in clear cell renal cell carcinoma (ccRCC) predicted worse disease-specific survival (DSS) and recurrence-free survival (RFS) and whether it was associated with more aggressive behavior in small renal masses.', 'In total, 703 ccRCC tumors were analyzed using fluorescence in situ hybridization (316 tumors) and cytogenetics (388 tumors). Tumor grade, classification, and size; 9p status; Eastern Cooperative Oncology Group performance status (ECOG PS); lymph node involvement; and the presence of metastasis were recorded. Outcomes were stratified by 9p status, and a Cox proportional hazards models was constructed using TNM staging, ECOG PS, tumor size, tumor grade, and 9p status.', 'Deletions of 9p were detected in 97 tumors (13.8%). At presentation, 9p-deleted tumors were larger and were more likely to be high grade (grade 3 or 4), to have a high tumor (T) classification (T3-T4), and to have lymph node or distant metastases (P < .01). The median DSS for patients with and without 9p deletions was 37 months and 82 months, respectively (P < .01). In patients with localized disease, the median RFS in those who had 9p deletions was 53 months and was not reached in those without 9p deletions (P < .01). In patients who had localized lesions that measured ≤4 cm in greatest dimension, 9p-deleted tumors were more likely to recur (19% vs 2%; P = .01).'] Do chromosome 9p deletions identify an aggressive phenotype of clear cell renal cell carcinoma?