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Farmers in the southern Kilimanjaro region of Tanzania have a strong preference for maize as their staple crop and have resisted attempts to introduce sorghum as an alternative in spite of the high drought risk associated with maize production. This paper presents the results of a seven-year period of field experiments to assess the benefits of a modified cropping system for maize, which aims to reduce drought risk through rainwater harvesting. In-situ, microcatchment and macrocatchment rainwater harvesting systems were tested against the local practice of flat cultivation as control. All were managed according to local extension recommendations, and the benefits were measured in terms of grain yield. In-situ rainwater harvesting provided no benefit. Microcatchment rainwater harvesting resulted in increased yield per unit area cultivated. On a total system area basis (i.e. including the uncropped catchment), however, production decreases were observed. A cost-benefit analysis, however, does show a benefit in the short rainy season. Macrocatchment rainwater harvesting provided increases in grain yield in both the short and the long rainy seasons.