To compare frequency and degree of orthostatic hypotension (OH) in Parkinson's disease (PD) and Parkinson's disease with dementia (PDD) and its effect on attention and word fluency, blood pressure (BP) and heart rate changes during tilt were determined in 10 PD and 8 PDD patients. Attention and word fluency were evaluated in supine and tilted position using standard neuropsychological tests. OH defined as systolic BP (SBP) drop of >/=20 mmHg and/or diastolic BP (DBP) drop of >/=10 mmHg was present in 5 PDD patients and in 2 PD patients. SBP drop was significantly greater in PDD than in PD patients (P < 0.05). Whereas word fluency was unaffected by tilt in both patient groups, attention as assessed with the Test of Everyday Attention (TEA) deteriorated significantly in the PDD group, correlating with blood pressure response (DeltaSBP and TEA-2, r = 0.828, P < 0.05; DeltaDBP and TEA-2, r = 0.828, P < 0.05). We conclude that OH is frequent in PDD and should be addressed therapeutically since it may exacerbate attentional dysfunction.