We present a patient with familial brachial plexus neuropathy (FBPN) who is in the second generation of a family found to have this disease. The patient suffered phrenic paralysis, which has only been previously described in association with FBPN in 4 similar cases, all of which also involved the left phrenic nerve. The side of phrenic paralysis's was unrelated to the side where brachial plexus lesions occurred. We believe that paralysis of the diaphragm, although rare, can be considered a sign of FBPN and that therefore this disease should be included in the differential diagnosis of such paralysis. This is particularly so whenever family or personal history suggest that the peripheral nervous system may be involved, compromising the brachial plexus, or whenever facial or digital dysmorphia is present.