The importance of the occlusion test is analysed in patients who were operated for a decompensating exophoria or an intermittent exotropia. Of particular interest before and after the occlusion test was the number of the following variables: the distant angle, the near angle, the difference between these two (the so-called distant angle-near angle difference), and the angle at right respective left gaze. All patients included in this study had been examined at least three times preoperatively. The occlusion test was performed in all patients by occluding one eye on three consecutive days. A total of 36 patients with decompensating exophoria and 33 patients with intermittent exotropia were included in this retrospective clinical trial. Only the near angles of the patients with the decompensating exophorias demonstrated a statistically significant increase. All the other angles did not show a significant change. In contrast to what might have been expected, the difference between the distant angle and the near angle increased in the exophoria group. This was not the case in patients with intermittent exotropia. Thus the occlusion test cannot generally be recommended as an obligatory part of the preoperative diagnostics in patients with exophoria or intermittent exotropia. In selected cases it may however be worthwhile to decide on the exact extent of the operation planned.