The low adoption of improved technologies by farmers has been identified as one of the major factors affecting agricultural production and food security in many developing countries including Ghana. Farmer-based organizations have been identified as important channels for information and technology dissemination to farmers. The effect of these groups on farmers’ adoption decisions has important implications for agricultural production and food security in many developing countries. This study therefore sought to examine the effect of farmer group membership on improved variety adoption by smallholder maize farmers in the Tolon District of Ghana using cross-sectional data from a sample of 160 farmers. A recursive bivariate probit (RBP) model was used to estimate the effect of group membership on adoption. The results indicate that membership in farmer groups is associated with lower adoption of improved maize varieties, which is contrary to generally held view that farmer groups promote adoption by farmers. Adoption is higher for the married and farmers with access to agricultural extension but decreases with size of herd size and cultivated land. The results underscore challenges confronting farmer-based organizations such as increasing politicization, decreasing effectiveness, and lack of support from both public and private institutions. Incentivizing farmer groups, including the apex body responsible for supervision of these groups will enhance effectiveness of farmer groups.