Minority migrant populations, such as older Samoan women, are likely to underuse preventive health services, including mammography screening. The purpose of this paper is to explore how informal (lay peers from churches) and formal (health care providers) health communication networks influence mammography screening use among older Samoan women. To do so, we apply diffusion of innovation theory and network analysis to understand how interpersonal networks may affect mammography use in this urban-dwelling, migrant population. The data come from a survey of 260 Samoan women, aged 50 years or older, who attended 39 randomly sampled Samoan churches in Los Angeles County (USA) between 1996 and 1997. Retrospective data, based over a 20-year period from this sample's year of first use of mammography screening, suggest that interpersonal networks may have accounted for the dramatic increase in the rate of adoption within the past 5 years of the survey. Using this information, we categorized women into mutually exclusive stages of mammography use and regressed these stages of mammography use on formal (had a provider referral) and informal (level of connectedness with peers in churches) health communication networks. The results indicated that being well-connected within women's informal, church-based health communication networks increased the likelihood of being in the decision (planned to have) and implementation and confirmation (had a recent mammogram) stages, but having a provider referral for a mammogram (formal networks) only increased the likelihood of being in the latter stages compared to women in the knowledge and persuasion stages. Formal and informal health communication networks influence recent use of mammography screening, but informal networks, in and of themselves, are also influential on future intention to use mammography screening.