Human polo-like kinase 1 (PLK1) plays an important role in the control of mitotic progression and in the maturation of centrosomes. Its overexpression has been observed in a variety of malignancies including colorectal cancer and PLK1 expression level has been shown to correlate with clinical outcome, with decreased expression associated with tumour regression and decreased local recurrence. Patients who had undergone primary surgery for rectal or rectosigmoid cancers were selected from our pathology database from 2000-2010, and tissue microarrays constructed from formalin-fixed paraffin-embedded tissues. Samples obtained from the cancer centre (CC) and cancer periphery (CP) were stained for PLK1 by immunohistochemistry. The percentage of positive cells and staining intensity were scored and these two measures multiplied to give weighted scores ranging from 1-12, dichotomised into low (0-5) or high (6-12). CC and CP scores were also averaged (CCCP). Paired t-test was used to compare PLK1 in CC and CP, Fisher’s exact test for associations between PLK1 and clinicopathologic variables, and Kaplan Meier for survival. 351 cases were identified with a median age of 72, 36% female, 64% male, 34% T1/2, 66% T3/4, 45% node-positive and 7% metastatic. OS was 3.2 years. 24% had neoadjuvant and 31% adjuvant treatment. The median PLK1 score was 3 for CC and 4 for CP. These scores were significantly different (p-value<0.001). Correlation was found between low CP PLK1 and presence of metastases (p=0.001). Kaplan Meier analysis revealed CCCP PLK1 to be significant for overall survival (p=0.047), with lower scores corresponding to improved survival. PLK1 scores in CC and CP are significantly different and the average score may have better clinical utility, with lower scores associated with improved outcome. The significance of the association between CP PLK1 and metastatic disease is unclear and needs to be further explored.