This research article published by Hindawi, 2017The study aimed at assessing water, sanitation, and hygiene practices and their influence on infectious diseases among under-five children in semipastoral communities of Arusha. The study was cross-sectional in design. Prevalence of infectious diseases among under-five children was derived from patients' attendance register. Mothers randomly sampled from households were interviewed using questionnaire. Information regarding child morbidity and sociodemographic and WASH characteristics was gathered. Hospital data revealed that 2/3 of under-five patients visited the hospitals annually were suffering from infectious diseases. Mean percentage of diarrhea prevalence for years 2013-2015 in Longido was higher than the mean of the respective years prevalence in Monduli ( = 0.02). Households' survey showed that 15.5% of under-five children were suffering from diarrhea. Children who consumed foods kept in ( < 0.001) or used unboiled cows' milk ( = 0.01) or were drinking surface water ( = 0.04) or born to uneducated mothers ( = 0.01) had increased risk of developing diarrhea compared to their counterparts. Storing complementary foods in was strongly associated with diarrhea among under-five children. To address the problem, communities under study need to be motivated through health education on food hygiene, proper handling of food storage containers, and domestic water treatment at the household level.