['To examine whether pathological tumour diameter assists in predicting conventional vs other histological subtypes in renal cortical tumours (RCTs) of <or=4 cm diameter.', "In all, 393 patients from Columbia University's Comprehensive Urologic Oncology Database who underwent radical or partial nephrectomy between 1988 and 2005 and had RCTs of <or=4 cm were analysed. Logistic regression analysis using tumour diameter as a continuous variable was used to determine whether size predicted histological subtype. Odds ratios (ORs) were calculated to estimate the likelihood of having conventional histology based on diameter.", 'The median patient age at surgery was 64.3 years and median tumour diameter was 3 cm, In all, 256 (65.1%) of the RCTs were conventional subtype and 137 (34.9%) were nonconventional. Logistic regression analysis showed that for every 1 cm increase in diameter up to 4 cm, the RCT was 1.27 times more likely to be conventional (P = 0.020). The ORs showed that a 4-cm RCT was 2.06 times more likely to be conventional than tumours of 0.6-1.5 cm.'] Does pathological tumour diameter predict risk of conventional subtype in small renal cortical tumours?