The pelvic floor musculature plays an important role in behaviors such as defecation, micturition, mating behavior, and vomiting. A recent positron emission tomography (PET) study revealed that structures belonging to the emotional motor system are involved in the control of the pelvic floor during micturition. However, there also exist brain structures involved in the voluntary motor control of the pelvic floor, and the present PET study was designed to identify these structures. Six adult female volunteers were scanned with the bolus injection of H 2 15 O during the following four conditions: (1) rest, (2) repetitive pelvic floor straining, (3) sustained pelvic floor straining, and (4) sustained abdominal straining. The results revealed that the superomedial precentral gyrus, the most medial portion of the motor cortex, is activated during pelvic floor contraction and the superolateral precentral gyrus during contraction of the abdominal musculature. In these conditions, significant activations were also found in the cerebellum, supplementary motor cortex, and thalamus. The right anterior cingulate gyrus was activated during sustained pelvic floor straining. No activations were found in subcortical structures belonging to the emotional motor system. The results are discussed in light of the existing literature on human control of the pelvic floor and micturition.