Objective: The cost of implementing professionally-led psychosocial interventions has limited their integration into routine care. To enhance the translation of effective psychosocial interventions in routine care, a self-administered format is sometimes used. The meta-analysis examined the efficacy of written self-administered, psychosocial interventions to improve outcomes among individuals with a physical illness. Methods: Studies comparing a written self-administered intervention to a control group were identified through electronic databases searching. Pooled effect sizes were calculated across follow-up time points using random-effects models. Studies were also categorised according to three levels of guidance (self-administered, minimal contact, or guided) to examine the effect of this variable on outcomes. Results: Forty manuscripts were retained for the descriptive review and 28 for the meta-analysis. Findings were significant for anxiety, depression, distress, and self-efficacy. Results were not significant for quality of life and related domains as well as coping. Purely self-administered interventions were efficacious for depression, distress, and self-efficacy; only guided interventions had an impact on anxiety. Conclusions: Findings showed that written self-administered interventions show promise across a number of outcomes. Practice implications: Self-administered interventions are a potentially efficacious and cost-effective approach to address some of the most common needs of patients with a physical illness.