Abstract: The aim of this study was to identify the characteristics of clinically insignificant prostate cancer in autopsy material. It was examined that the histological characteristics (tumor volume and Gleason score) of stage T1a carcinomas found in autopsy among 40 impalpable (hypothetical stage T1) carcinomas of the prostate of 212 men between 30 and 98 years who died of diseases other than carcinoma of the prostate and related conditions. Other pathological features (capsular penetration, perineural and perivascular invasion) were also examined and cross-correlated with histological differentiation and tumor volume of the 40 cancers, 36 occupied less than the 5% of the total volume of the prostate gland and would be classified as of stage T1a if diagnosed during lifetime. Twenty seven (75%) out of 36 hypothetical T1a cases had favourable histological features (relatively low volume, Gleason score between 2 and 6 and absence of invasiveness). The lowest volume tumours were those of low and intermediate grade (Gleason sums 2 through 6). Among tumours with volumes of less than 1 cc, 96.55% were confined within the prostatic capsule. According to present findings as insignificant T1a tumours could be considered those of volumes of less than 1 cc and Gleason sums 2 through 6.