Background: Surgical site infections are infections that occur at or near surgical incision within 30 days of operation or within 1 year if implant is placed. The incidence varies from hospital to hospital. Several factors affect the development of surgical site infections. Even though the extent of surgical site infection in Ethiopia is high, there are no published studies on abdominal surgical site infection and no baseline information regarding SSI in Bichena Primary Hospital, North West Ethiopia. Objective: The aim of the study was to assess the magnitude and associated factors of surgical site infections among abdominal operated patients in Bichena primary Hospital, Bichena Town, East Gojjam Zone, Amhara Region, Ethiopia, 2022. Methods: A hospital based retrospective cross sectional study was conducted among all abdominal operated patients in two years. The sample size was computed for single population proportion magnitude of surgical site infection and the sample size was estimated to be 163. Adding 10%contingency a total 183 was the total sample size required. A pre-designated and pretested check list was used to collect the data. The data was collected by 2 BSc nurses trained for the data collection using a checklist prepared for the data collection. Data was analyzed using Epi-data version3.1.1 and export to SPSS 22.0 software for descriptive statistics and regression and the level of confidence was p-value<0.05. Results: Among the total of 164 patients who had abdominal operation, the total magnitude of SSI was 44(26.8%) and with 95% confidence the true estimate lays between 20.1% to 33.5%.On multivariate logistic regression and with 95% confidence the true estimate lays between (95%CI:[20.1%-33.5%]). On multivariate logistic regression analysis Patients with associated medical illness was 3.38 times more likely to develop SSI than those who do not have associated medical illness AOR=3.375(95%CI: [1.325,8.599,p<0.001]), and Patients admitted 5-7 days 91.1% times less likely AOR=0.089(95%CI: [0.076,0.953,p=0.002]), 8-14days 78.3% times less likely AOR=0.217(95%CI:[0.078,0.754,p=0.005]),and 15-21 days 72.4% times less likely AOR=0.276(95%CI: [0.047,0.599,p=0.001]) to develop surgical site infection than as compared to >=22days of post operative admissions. Conclusion:The magnitude of SSI in the study institution was high.Surgical site infection is a major drain on hospitals catering to a high volume of patients. Associated medical illness and longer hospital stay were the important factors for development of surgical site infection.