Crossed cerebellar diaschisis (CCD) was investigated in a series of 59 patients (34 completed strokes and 25 reversible ischemic attacks, RIAs) using single photon emission computerized tomography (SPECT) with 123I-HIPDM as a cerebral blood flow (CBF) indicator. CCD was present in 17 (50%) of the patients with completed stroke and in 6 (24%) of the patients with RIAs. CCD was significantly correlated to the clinical severity (p < 0.001) and to the extension of the supratentorial lesion (p < 0.05). However, CCD was also recorded in 3 out of 16 patients with normal neurological examination and CT scan, suggesting that a ‘functional’ hemispheric disturbance may be sufficient to produce a remote effect on the contralateral cerebellar hemisphere. Time elapsed between the clinical onset and SPECT study was not critical, since CCD was recorded in the acute as well as in chronic studies. Follow-up SPECT studies showed that CCD disappeared in 5 out of 18 patients after a successful extra-intracranial bypass, while a spontaneous recovery was observed in only one of 16 nonsurgical patie