The spatial scale over which changes in neural activity influence local blood flow remains under debate. Here, blood vessel diameter and adjacent neuronal spiking activity in the cat visual cortex were monitored simultaneously during exposure of the animal to a range of stimulus orientations. Parenchymal vessel responses showed the same orientation selectivity as the surrounding neural tissue, but vascular dilation also occurred when there was little adjacent neural activity. This suggests that vessel responses do not precisely reflect the activity of adjacent neurons and operate over a wider spatial scale.