The development, adoption and acceptance of eHealth systems in changing and improving patient self-care has been promising, but the results have been mixed, and the work mostly atheoretical. This paper responds to this opportunity by developing and assessing an eHealth system for newly diagnosed type 2 diabetes patients. Study participants used the eHealth system for a 12-month period after diagnosis in an attempt to acquire an understanding about their diabetes, to develop self-care activities, and to improve their biomedical outcomes. Drawing upon theories and methods from information systems, and the Precede-Proceed model of health promotion planning, the paper explores the 'double adoption' of eHealth technology and its antecedents, self-care practices and their antecedents, and improvements in biomedical outcomes important to long-term diabetes health. Path model results indicate important implications for IS, eHealth and health promotion practice and research, which are discussed.