Hypotheses: Task performance improves with the use of a balanced degree of shadow and illumination compared with no or maximum shadow contrast; and overhead shadow-casting illumination is better than side illumination. Design: The standard task entailed touching target points on an undulating surface by using a surgical hook. Each run consisted of 13 target points in a random sequence. Five settings were investigated: no shadow; 22%, 42%, and 65% shadow contrast created by overhead

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... and 22% shadow contrast produced by side illumination. Each surgeon completed 3 runs with each setting in a random order. Setting: Research laboratory at the Surgical Skills Unit, Ninewells Hospital, Dundee, Scotland. Participants: Ten surgical trainees. Main Outcome Measures: Number of errors and execution time. Results: Shadow contrast settings had fewer errors than shadowless imaging (PϽ.001). Work with overhead 22% shadow contrast had a lower error rate than side illumination (PϽ.001). With overhead illumination, 22% and 42% shadow contrast were accompanied by a lower error rate than maximum shadow contrast of 65% (PϽ.001 and P=.005, respectively). No significant difference was found in the execution time. Conclusion: Optimum endoscopic task performance is obtained with overhead shadow-casting illumination and a balanced degree of illumination and shadow contrast.