Background In the operating room, factors such as interruptions, communication failures, team familiarity and the unpredictability of unplanned cases can prolong the length of an operation, and lead to inefficiency and increased costs. However, little is known about the extent to which such factors contribute to extending the expected length of an operation. Aim To describe factors that prolong the expected length of an operation. Methods Structured observations were performed on a purposive sample of 160 surgical procedures across 10 specialties of planned and unplanned surgeries. During the 6-month period, a trained observer structured observations. Bivariate correlations and a standard multiple regression model were developed to describe associations among unplanned operations, interruptions, prebriefings, team familiarity, communication failures and the outcome, and deviation from expected operation time. Results Of the three explanatory variables entered into the regression model, the only significant predictor of deviation in expected length of operation was the number of communication failures (p=0.013). This model explained 4.5% of the variance in deviation in expected length of operation (p=0.018). Conclusions The results of this study validate the role of prospective observational research methods in unveiling critical factors that contribute to deviation in expected length of operation. These results have the potential to inform evidence-based interventions aimed at ameliorating the effects of miscommunications, hence improve patient safety.