<p><b>Background</b> Evidence suggests that up to 30% of cancer patients may meet the criteria for adjustment disorder. However, no assessment instruments have been validated for use with cancer patients. The Adjustment Disorder New Module (ADNM)-8 and ADNM-4 are brief screening tools for adjustment disorder mapped directly to the new ICD-11 criteria. The aim of this study was to investigate the factor structure and validity of both instruments in an Australian sample of adult oncology patients.</p> <p><b>Methods</b> A total of 405 participants with a cancer diagnosis were recruited online from across Australia. Participants reported cancer-specific information, such as time since diagnosis, treatment stage, cancer stage, type of cancer, and the following questionnaires: 8-item Adjustment Disorder New Module (ADNM-8), the World Health Organisation Well-Being Index (WHO-5), and the short form Depression Anxiety and Stress Scale (DASS-21). The predictiveness of stressors was assessed using multiple regression analysis and the structure of the ADNM-8 and the ADNM-4 was tested using confirmatory factor analysis.</p> <p><b>Results</b> Six previously tested models were examined, and the results suggested a 2-factor structure reflecting the two ICD-11 diagnostic criteria clusters of preoccupation with the stressor and failure to adapt was a good ft for both scales. The ADNM-4 outperformed the longer version of the scale on numerous ft indices though the ADNM-8 and ADNM-4 were highly correlated. Correlations of both scales with the psychological distress scale, the stress subscale, and the wellbeing index indicated good construct validity.</p> <p><b>Conclusions</b> Our results suggest that the ADNM-8 and ADNM-4 are useful screening tools for assessing adjustment disorder symptoms in cancer patients. The prompt screening of cancer patients encourages early intervention for those at risk of adaptation difficulties and informs research and clinical decisions regarding appropriate treatments.</p>