Hospitals across the country are facing increases in hospital length of stay ranging from 2% to 14%. This results in patients who stay in hospital for long periods of time being three times more likely to die in hospital. Therefore, identifying factors that contribute to longer hospital stays enhances the ability to improve services and quality of patient care. However, there is limited documented evidence on factors associated with longer hospital stays among surgical inpatients in Ethiopia and the study area. This study aimed to assess the length of hospital stay and associated factors among adult surgical patients admitted to surgical wards in Amhara Regional State Comprehensive Specialized Hospitals, Ethiopia, 2023. An institutional-based cross-sectional study was conducted among 452 adult surgical patients from April 17 to May 22, 2023. Data were collected based on a pretested, structured, interviewer-administered questionnaire, medical record review, and direct measurement of BMI. Study participants were selected using a systematic random sampling technique. The collected data were cleaned, entered into EpiData version 4.6.0 and exported to STATA version 14 for analysis. Binary logistic regression analysis was used. Variables with a p value <0.05 in the multivariable logistic regression analysis were considered statistically significant. In the current study, the prevalence of prolonged hospital stay was 26.5% (95% CI: 22.7, 30.8). Patients referred from another public health facility (AOR = 2.65; 95% CI: 1.14, 6.14), hospital-acquired pneumonia (AOR = 3.64; 95% CI: 1.43, 9.23), duration of surgery ≥110 minutes (AOR = 2.54; 95% CI: 1.25, 5.16), being underweight (AOR = 5.21; 95%CI: 2.63, 10.33) and preoperative anemia (AOR = 3.22; 95% CI: 1.77, 5.86) were factors associated with prolonged hospital stays. This study found a significant proportion of prolonged hospital stays among patients admitted to surgical wards. Patients referred from another public health facility, preoperative anemia, underweight, duration of surgery ≥110 minutes, and hospital-acquired pneumonia were factors associated with prolonged hospital stay. Early screening and treatment of anemia and malnutrition before surgery can shorten the length of stay.