Social network sites (SNSs) are growing in popularity and social significance. Although researchers have attempted to explain the effect of SNS use on users' psychological well‐being, previous studies have produced inconsistent results. In addition, most previous studies relied on healthy students as participants; other cohorts of SNSs users, in particular people living with serious health conditions, have been neglected. In this study, we carried out semistructured interviews with users of the Ovarian Cancer Australia (OCA) Facebook to assess how and in what ways SNS use impacts their psychological well‐being. A theoretical model was proposed to develop a better understanding of the relationships between SNS use and the psychological well‐being of cancer patients. Analysis of data collected through a subsequent quantitative survey confirmed the theoretical model and empirically revealed the extent to which SNS use impacts the psychological well‐being of cancer patients. Findings showed the use of OCA Facebook enhances social support, enriches the experience of social connectedness, develops social presence and learning and ultimately improves the psychological well‐being of cancer patients.