To study the value and the proper timing of vitrectomy in cases of ocular trauma involving the posterior segment, 24 rabbit eyes were traumatized by introducing a steel foreign body and autogenous blood into the vitreous. Twelve eyes underwent vitrectomy, 6 in the first week after trauma ("early") and 6 in the fourth week ("late"). The other 12 eyes, which underwent removal of the foreign body but not vitrectomy, served as controls. Traction retinal detachment did not develop in the 6 early-vitrectomy eyes, but it did occur before vitrectomy in 4 of the 6 eyes of the late-vitrectomy group and in 6 of the 12 control eyes. Iatrogenic cataract and retinal breaks were twice as frequent in the late as in the early group. The data seem to favor early vitrectomy in eyes with posterior-segment trauma. However, in routine clinical practice we advise prompt primary repair and exploration to evaluate the extent of posterior-segment damage, and vitrectomy within 14 days after injury.