This article has considered the subject of bony pelvic dystocia and soft tissue dystocia. Dystocia most often results from a combination of fetal and pelvic factors. However, on many occasions the size and shape of the pelvis is the initial problem, which encourages the fetus to take up a malposition such as occiput-posterior, and this in turn results in a dysfunctional contraction pattern that may or may not be corrected by oxytocin augmentation--a vicious circle that can only be broken by performance of a cesarean section. With minor degrees of pelvic dystocia, asynclitism and molding of the fetal head can often make a safe vaginal delivery possible. Clinically all pelvises can be categorized into adequate, questionable, and too small. The latter group is the least common and generally includes the congenitally or developmentally abnormal pelvises, and in most cases primary cesarean section should be the mode of delivery. In all other pelvises with a vertex presentation, a trial of labor is indicated because the fetal head is an excellent pelvimeter. With proper fetal monitoring with an intrauterine pressure catheter, with the use of a partograph to assist in the diagnosis of an active-phase arrest, followed by a cesarean section at the appropriate time, there is no increase in fetal or maternal morbidity. If the breech is the presenting part, then there are only two types of pelvis--very adequate and inadequate--and x-ray pelvimetry should be used to help in the classification.(ABSTRACT TRUNCATED AT 250 WORDS)