Fifty patients from rural areas in the Jenin district of the West Bank, Palestinian Authority, were diagnosed with visceral leishmaniasis (VL) between 1989 and 1998. Forty-nine (98%) were younger than 6 years old, the youngest being 9 months. The yearly incident rate of VL in the Jenin district was highest in 1994 (11.8/100,000) and decreased to 1.5/100,000 in 1998; a mortality rate of 4% was recorded. Seventeen (5.5%) of 308 dogs from the Jenin and Ramallah districts of the West Bank were seropositive by enzyme-linked immunosorbent assay in a survey of canine leishmaniasis. Although all the leishmanial strains cultured from humans and dogs were identified as Leishmania infantum by a species-specific polymerase chain reaction, further genetic analysis by restriction fragment length polymorphism of kinetoplast DNA revealed patterns of polymorphism within isolates. The findings indicate that an active focus of potentially fatal VL exits in the Jenin district of the West Bank and that the parasite, vector, and reservoir host are found in this area. The epidemiology of VL in that vicinity follows the pattern of a predominantly infantile disease traditionally found in Middle Eastern countries, without a considerable involvement of immunocompromised adults infected with HIV virus as reported in other regions.