In an exploration of the natural history of post-kala-azar dermal leishmaniasis (PKDL), 134 residents of Sudan who had recently been diagnosed as cases of the disease were investigated. In each case, diagnosis had been based on clinical criteria, the temporal relationship between the rash and the treatment of visceral leishmaniasis (VL), positive results in direct agglutination tests (DAT) and/or leishmanin skin tests (LST), and the exclusion of other skin conditions. The mean (S.D.) age of the subjects was 6.4 (3.0) years. Although PKDL appeared commonest among those aged 4-8 years (P < 0.05), it was most severe in children aged <or= 3 years. Males and females were equally affected. The rash developed 0.5-13 months following the apparently successful treatment of VL, a relatively rapid onset being associated with severe disease (P = 0.01). The distribution of the rash on the body often reflected the clothing habits of the case, being most frequent on skin that was regularly exposed to the sun. Spontaneous healing of the lesions occurred within 12 months in the majority of cases, the PKDL lasting for a mean (S.D.) of 9.7 (4.7) months. Persistence of lesions beyond 1 year was significantly associated with the combination of a high titre in the DAT and a negative result in the LST (P < 0.05). In conclusion, spontaneous healing is commonly seen in Sudanese patients with PKDL. Persistence of the lesions is frequently associated with non-reactivity in the LST and high levels of anti-leishmanial antibodies.