Post kala-azar dermal leishmaniasis (PKDL) was studied in relation to the kala-azar epidemic in Bihar, India. Between 1970 and 1989, 530 individuals, 302 males and 228 females, were admitted to the hospital of Patna Medical College with PKDL, the number of cases steadily rising from two in 1970 to 59 in 1989. The age of the patients varied from four to 70 years, with 33% aged 11-20 years and 16% 0-10 years. The prevalence of kala-azar in India also increased in the same period, mostly as the result of an epidemic of the disease in Bihar. There were no cases of this disease admitted to Patna Medical College from 1958-1970, it having become rare in India in the 1950s, possibly as a result of the DDT sprayed during the National Malaria Eradication Programme. In the period 1977-1990, however, there were 301,076 cases of kala-azar reported in Bihar alone, with a mortality rate over 2% (compared with 31,074 cases and a mortality rate below 0.4% for the rest of India). It seems possible that, once DDT spraying stopped, the re-establishment of large sandfly population and infection of these vectors, largely as a result of them feeding on cases of PKDL, provoked the resurgence of kala-azar. The study emphasizes the need to search for cases of PKDL, even in young children, and to monitor and effectively treat them as part of kala-azar control programmes. All patients could be cured if treated with the right dosage for the right period.(ABSTRACT TRUNCATED AT 250 WORDS)