Due to beneficial characteristics of cassava such as robustness and versatility for multiple uses, it can have a major role in contributing to local food security. The objective of this study was to find out whether and how the cultivation of cassava benefits smallholder farmers in the regions of Dodoma and Morogoro, Tanzania. In addition, the study assessed the main factors that support or threaten food security of smallholder farmer households in the survey region and analysed whether cassava cultivation could counteract them. We applied a mixed methods approach. Quantitative data were provided by a comprehensive household survey of the Trans-SEC project, and qualitative data were collected by conducting semi-structured interviews. To approach the complexity of our chosen food security definition, three approaches for household food security measurement were applied. These covered the components of food availability, food access, and food utilization. Additionally, dependent variables for regression models were constructed and a multivariate analysis was run. The results show that cassava contributes to food security in the households, but achieving food security through cassava cultivation was constrained by several factors, including pests, missing markets, poor processing, social perception and lack of knowledge. Besides these, other factors affecting food security in the study area were found, uncovering some roots of local food insecurity and serving as a basis for further research and action on how to enhance food security.