This study was conducted to find out if the patterns of PTEN gene molecular aberration in colorectal carcinoma are consistent with the classic molecular features ascribed to a tumour suppressor gene. PTEN gene mutations and LOH were assayed in a series of 18 colorectal carcinomas. Three PTEN gene mutations were found in 1 tumour, complete loss of one allele(LOH)in 2 tumours and allelic imbalance (AI) in 6 tumours. LOH or AI did not target the 1 tumour with the PTEN gene mutations. The widely held belief of PTEN as a classical tumour suppressor gene is not supported by the findings from this study.