Background and Objectives: Involvement of lymph nodes is an important prognostic factor in the most cancers, including colorectal cancer. In the recent years, invasion to blood and lymphatic vessels has been shown to predict involvement of lymph nodes and the number of involved nodes has been less studied issue. The aim of this study was determination of the relationship between the size of colorectal adenocarcinoma and lymph node involvement. Materials & Methods: In this cross-sectional study, 116 patients were enrolled with colorectal cancer from Rasoul-e-Akram and Mehr Hospitals in 2002-2008. Data analysis was performed by SPSS-15 software. Results were expressed as frequency, percent, and mean ±SD. We used Chi2, student t-test and correlation tests for statistical analysis. Results: 54.3% of patients were male and 45.7% were female. Mean age of them was 59.4± 12.9 years. Mean of tumor size (longest diameter) was 5.4± 2.2 (range: 1.5 to 12) cm. Mean number of involved lymph nodes was 4.9± 3.5(range: 1-14). There was no correlation between number of lymph node involvement and tumor size. There was no correlation between lymph node involvement and tumor and age group, sex, location and depth of tumor. Poorly differentiated tumor significantly correlated to lymph node involvement (P=0.001). Conclusion: There is no correlation between tumor size and number of involved lymph node in colorectal cancer. However, poor histopathologic grade is associated with lymph node involvement.