Maize is a strategic commodity for improving food security and alleviating poverty in Tanzania, but its productivity remains low. The importance of improved maize varieties (IMVs) in increasing productivity is documented in existing literature. Previous adoption studies in Tanzania did not examine the factors that influence the speed/timing of adoption. This study examines the determinants of the speed of adoption of IMVs using a duration model and recently collected plot- and household-level data in rural Tanzania.