Post-kala-azar dermal leishmaniasis (PKDL) is a common complication following kala-azar (visceral leishmaniasis). In a prospective study in a village in the endemic area for kala-azar in the Sudan, 105 of 183 (57%) kala-azar patients developed PKDL. There was a significantly higher PKDL rate (69%) in those who received inadequate and irregular treatment of kala-azar than in those who were treated with stibogluconate 20 mg kg−1 daily for 15 days (35%). The group of patients who developed PKDL did not differ from those who did not develop PKDL with regard to age and sex distribution, reduction in spleen size, and conversion in the leishmanin skin test (LST). In a clinical study, 416 PKDL patients were analysed and divided according to grade of severity. Severe PKDL was more frequent in younger age groups (P < 0·001); there was an inverse correlation between grade and conversion in the LST (P < 0·01). In 16% of patients tested, parasites were demonstrated in inguinal lymph node or bone marrow aspirates, indicating still visceral disease (para-kala-azar dermal leishmaniasis); there was no correlation between the presence of parasites and grade of severity. Conversion rates in the LST were lower than in those who did not have demonstrable parasites (11% and 37%, respectively; P < 0·01). In the absence of reliable and practical diagnostic tests, PKDL may be diagnosed on clinical grounds and differentiated from other conditions, of which miliaria rubra was the most common. Differentiation from leprosy was most difficult.