Videocapillaroscopy (VCP) can be used to explore microcirculatory modifications in skin diseases. Psoriasis shows specific capillary alterations reflecting typical histopathological changes. To compare capillary morphology, distribution and density in psoriasis and seborrheic dermatitis of the scalp for differential diagnosis. VCP was performed on histology-confirmed scalp lesions of 30 patients with chronic plaque psoriasis, 30 age- and sex-matched patients with seborrheic dermatitis and 30 healthy subjects. The morphology, mean density per mm(2) and mean diameter of capillary loops was measured. Scalp psoriasis exhibited homogeneously tortuous and dilated capillaries (bushy pattern), with a 73 +/- 17 mum (mean +/- standard deviation) diameter of capillary bushes. In contrast, scalp seborrheic dermatitis presented a multiform pattern, with mildly tortuous capillary loops and isolated dilated capillaries, but a substantial preservation of local microangioarchitecture. Mean diameter of capillary bush was significantly lower (27 +/- 4 microm; p < 0.001) and similar to that of the scalp of healthy subjects (21 +/- 5 microm). Capillary loop density was similar in patients with psoriasis (23 +/- 5/mm(2)) seborrheic dermatitis (24 +/- 2/mm(2)) and healthy scalp skin (24 +/- 3/mm(2)). VCP could be a useful noninvasive approach for differentiating between psoriasis and seborrheic dermatitis, especially when the scalp is the only affected site.