Background: Malaria is one of the most serious health problems in Kenya. In 2004, the Kenya Medical Research Institute and the US Army Medical Research Unit - Kenya surveyed adults in Samburu, Malindi, and Busia districts to determine socioeconomic risk factors for infection. Methods: Sociodemographic, health, and antimalarial data were collected along with blood for malaria testing. A smear was considered negative only if no Plasmodium falciparum parasites were observed in 100 high-powered fields. Univariate analysis was performed with Pearson's Chi-square test and univariate logistic regression. A multivariate logistic regression model was then created which included only variables found to be at least marginally significant in univariate analysis. Results: A total of 1,141 subjects were recruited: 238 from Samburu, 442 from Malindi, and 461 from Busia. Smear positivities for P. falciparum were 1.7% in Samburu, 7.2% in Malindi and 22.3% in Busia. Interdistrict differences were statistically significant (p < 0.001) in univariate analysis and in a multivariate logistic regression model which included district, literacy, occupation, and recent illness as independent variables. In the model, literacy and recent diarrhoeal illness were positively and at least marginally significantly associated with parasitaemia (p = 0.023 and p = 0.067, respectively). Neither age, sex, occupation, history of malaria in the previous three months, nor use of antimalarials in the previous four weeks were significantly associated with parasitaemia. Conclusion: While district of residence was the variable most highly predictive for parasitaemia among Kenyan adults surveyed, both a recent history of diarrhoeal illness and literacy were at least marginally statistically significant predictors.