Background: Resilience is the ability to maintain or rapidly regain mental health during or after stressful life experiences. Cancer is a major risk factor for stress-associated mental illness. In this review, we attempt to identify effective resilience-promoting interventions in adults with cancer. Methods: The analysis was restricted to randomized, controlled trials of resilience-promoting interventions in adults with cancer in which training was provided for at least one psychosocial resilience factor. A selective search, with systematic components, for relevant publications was carried out in the PubMed and CENTRAL databases. Effect sizes (Hedges' g) were calculated wherever a fully reported dataset for resilience or post-traumatic growth was available. Results: Twenty-two trials with a total of 2,912 patients were included in the analysis; the intervention was provided in an individual setting in five trials and in group format in 17. Beneficial effects on resilience and post-traumatic growth, some of them large, were observed in patients who were acutely ill with cancer and after interventions that were provided in more than 12 sessions. The effect size ranged from g = 0.33 to g = 1.45. Largely beneficial effects were achieved by interventions based on the concepts of positive psychology, supportive-expressive group therapy, behavioral therapy, or mindfulness, with considerable variation in individual effect sizes. Conclusion: Interventions that promote resilience should be made available to interested and motivated cancer patients. These interventions should be provided, in parallel with somatic treatment, as soon as the diagnosis is made and should extend over more than 12 sessions whenever possible.