Respiratory manifestations of systemic lupus erythematosus (SLE) are frequent. They include respiratory muscle abnormalities, which have been implicated in the pathogenesis of the "shrinking lung syndrome" (SLS). We report the case of a patient with this syndrome, in whom diaphragmatic paralysis due to demyelinating phrenic lesions was diagnosed at the same time as SLE. Follow-up studies showed a favorable clinical and diaphragmatic outcome with corticosteroid therapy, but little change in spirometry. It is concluded that severe diaphragm palsy is possibly due to phrenic nerve lesions in SLE, and that the link between diaphragm dysfunction and the SLS is probably not a straightforward one.