The use of improved crop varieties is key to increasing food production, but in SubSaharan Africa traditional varieties still dominate smallholder farming. Lack of information is a major constraint to the adoption of improved varieties and the role of social networks in their diffusion is increasingly being studied. Social networks can, however, also affect the efficiency with which farmers use these technologies. In this paper we investigate the influence of social networks on technical efficiency of smallholder cereal producers. Using the case of Tanzania, we apply stochastic frontier analysis on data from sorghum and maize producers. Results show that the effects of social networks on efficiency differ by crop. Inter-village networks positively influence technical efficiency of improved sorghum varieties, but have no effect in case of maize. We further find that links to public extension officers increase efficiency of improved maize varieties. Some wider research and policy implications are discussed.