It is unclear whether crossed cerebellar diaschisis (CCD) is merely an epiphenomenon, as its clinical significance remains uncertain. We retrospectively analysed the positron emission tomographic (PET) findings in 28 patients with a chronic, stable middle cerebral artery (MCA) infarct and in 22 controls, using the steady state technique and 15O. Also, the Orgogozo scores on admission and at the time of the PET examination were compared in the patients with MCA infarction. Based on the asymmetry index and the 95% confidence limits for regional cerebellar blood flow (rCBF) and oxygen consumption (rCMRO2) in the control group, the stroke patients were subdivided in a group with (n = 8) and a group without (n = 20) CCD. The CCD group had lower values of rCMRO2 in the infarct and border areas compared to those of the non-CCD patients. The infarct location within the MCA territory was similar but the size was somewhat larger in the CCC group. The degree of neurological improvement was better in the non-CCD group. Although persistence of CCD has no real clinical significance it appears to be correlated to more severe and widespread ischaemia in the affected MCA territory and to the lack of significant clinical improvement.