BACKGROUND: Evidence on the efficacy of psychological interventions targeting cancer patients diagnosed with an adjustment disorder is scarce. AIMS: This study aimed to investigate the efficacy and budget impact of a tailored psychological intervention program (AD-program) targeting cancer patients with adjustment disorder (AD). METHODS: Patients (n = 59) were randomised to the intervention or control group. The AD-program consisted of three modules: psychoeducation (1-4 sessions) and two additional modules (maximum of 6 sessions per module) provided when needed. The primary outcome was psychological distress (HADS). Secondary outcomes were mental adjustment to cancer (MAC) and health-related quality of life (EORTC QLQ-C30). Measures were completed at baseline and 3 and 6 months after randomisation. The budget impact analyses were based on the population size, the costs of the AD-program, and other costs potentially affected by the AD-program. RESULTS: The mean psychological distress score in the intervention group (n = 33) decreased over time (M = 19.2 at T0, M = 15.6 at T6). This decrease was not significantly different from decrease in the control condition (n = 26, M = 17.5 at T0, M = 15.9 at T6, p >
0.05). Also, there were no significant differences between the two conditions on the secondary outcomes. The budget impact of the AD-program was estimated at 7-28 million euros per year (to treat 14,430 patients). CONCLUSIONS: The effect of the AD-program was not statistically significant in this RCT. Limitations include that this study was underpowered due to recruitment difficulties during the COVID-19 pandemic. More research on the efficacy and implementation of the AD-program is warranted. TRIAL REGISTRATION: Netherlands Trial Register identifier: NL7763. Registered on 3 June 2019.