In recent years, vitamin D3 analogues have become one of the most widely prescribed topical treatments for mild or moderate chronic plaque psoriasis. These molecules are effective and safe, but their exact mechanism of action is not completely understood. In vitro studies have shown that D3 analogues decrease proliferation and induce differentiation of keratinocytes, and have strong immunomodulating effects, but there are no conclusive data about apoptosis. The aim of this study was to evaluate differences in apoptotic response between lesional and perilesional keratinocytes of patients with psoriasis before and after treatment with calcipotriol, a synthetic vitamin D3 analogue. Keratinocytes were isolated from psoriatic plaques including lesional and perilesional skin, and cultured. Cells were treated with calcipotriol for 20 h and examined under confocal microscopy after staining with propidium iodide. The number of apoptotic cells after incubation with calcipotriol was significantly higher in lesional than in perilesional keratinocytes (P < 0.05) or non-treated psoriatic keratinocytes (P < 0.05). In conclusion, calcipotriol seems to induce apoptosis in psoriatic keratinocytes.