We studied whether reported physical activity and measurements of fitness (hand, leg and inspiration) were associated with postoperative in-hospital mortality, length of stay and discharge destination in 169 patients after major oncological abdominal surgery. In multivariate analysis, adequate activity level (OR 5.5, 95% CI 1.4–21.9) and inspiratory muscle endurance (OR 5.2, 95% CI 1.4–19.1) were independently associated with short-term mortality, whereas conventional factors, such as age and heart disease, were not. Adequate activity level (OR 6.7, 95% CI 1.4–3.0) was also independently associated with discharge destination. The factors that were independently associated with a shorter length of hospital stay were as follows: absence of chronic obstructive pulmonary disease (HR 0.6, 95% CI 0.3–1.1); adequate activity level (HR 0.6, 95% CI 0.4–0.8); and inspiratory muscle strength (HR 0.6, 95% CI 0.5–0.9). For all postoperative outcomes physical activity and fitness significantly improved the predictive value compared with known risk factors, such as age and comorbidities. We conclude that pre-operative questionnaires of physical activity and measurements of fitness contribute to the prediction of postoperative outcomes.