Cathepsin B is a lysosomal cysteine proteinase associated with degradation of laminin. It is increased in colorectal carcinoma (CA). Laminin is a major component of basement membrane involved in cell-matrix interactions and tumor progression. The aim of this study was to correlate cathepsin B and tumor-associated laminin in colorectal adenomas (ADs) with increasing grades of dysplasia and in invasive CAs. Forty-five ADs (8 tubular, 16 tubulovillous, 21 villous), 13 adenomas with high-grade dysplasia/carcinoma in situ (AHDs), and 17 invasive CAs were immunostained with polyclonal antibodies to cathepsin B and laminin. Statistical analysis was performed using exact linear by linear association test and Spearman rank correlation coefficient. Cathepsin B-positive tumor cells were seen in 30 (67%) ADs, 13 (100%) AHDs, and 17 (100%) CAs. The grade of cathepsin B staining was significantly increased in AHDs and CAs, compared with ADs (P < .0001). Laminin was continuous in all of the ADs and discontinuous or fragmented in the AHDs and CAs (P < .0001). The degree of cathepsin B staining in tumor cells also correlated with breakdown of laminin. Increased cathepsin B expression and decrease in tumor-associated laminin might suggest a mechanism for progression of ADs to CAs.