Women following the stress resulting from the diagnosis and treatment for breast cancer draw resources from their network of friends and relatives. These resources include both emotional support and instrumental resources such as getting a ride to a medical appointment. Emotional support buffers the effects of the stresses they face and improves their mental well-being while the existence, rather than the use, of instrumental supports is positively related to physical well-being. These hypotheses are tested on a population-based cohort of 336 women in the United States, diagnosed and treated for breast cancer when aged 50 or less. Most are married (65%), work (75%), have dependent children (63%), are white (70%), and had a mastectomy (51%). Results of the multi-variate analyses indicate that consistent with predictions, controlling for socio-demographic and treatment-related variables, the size of the social network was related to greater emotional and instrumental support, and greater emotional support was related to better mental well-being. Contrary to predictions, greater use of instrumental resources was related to poorer physical well-being. The results indicate the importance of social resources on well-being following life-threatening illness.