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BACKGROUND: The forested hilly and foothill regions of north-east India are highly endemic for malaria and have a distinct epidemiological pattern. Nearly half the reported cases of malaria are from these areas. A knowledge of the risk factors in this eco-geographic entity may be helpful in formulating a specific control strategy. Hence, we conducted a community-based epidemiological study in a hilly, forested terrain of Arunachal Pradesh and examined different socio-demographic factors to identify those predisposing to the occurrence of malaria, especially Plasmodium falciparum infection, in such areas. METHODS: Four epidemiological surveys were carried out during 1997 in 7 villages located at the fringes of a forest (total population: 1177) under Nompong Primary Health Centre of Changlang district, Arunachal Pradesh. Blood slides were collected randomly from the inhabitants, irrespective of their fever status, ensuring at least 50% coverage. One hundred and thirty-four microscopically confirmed Plasmodium falciparum cases were identified and 536 controls were randomly selected from the list of uninfected inhabitants. Relevant socio-demographic information was obtained from both cases and controls. The data were analysed by simple and multiple logistic regression using the unconditional maximum likelihood method. RESULTS: Factors which were found to be strongly associated with Plasmodium falciparum malaria on univariate analysis were age, ethnicity, village of residence and accessibility to the nearest health care facility. However, in multiple regression analysis, after controlling for the effects of confounding variables, the only risk factor identified was accessibility to the nearest health care facility (adjusted odds ratio: 4.5; 95% CI: 1.8-11.3; p < 0.0001 for those at a distance of 2-8 km and adjusted odds ratio: 11.1; 95% CI: 4.1-30.0; p < 0.0001 for those > 8 km away). CONCLUSION: Distance, particularly non-motorable distance, from the place of residence to the nearest health care facility was a major risk factor for malaria in this hilly forested terrain. This indicates the need for special efforts to detect cases early and institute treatment promptly in such areas of the north-eastern region, so as to reduce the morbidity and mortality of malaria.