Marital adjustment plays a key role in the physical and psychosocial wellbeing. We conducted a cross-sectional study to evaluate marital adjustment and its association with psychological distress, suicidal ideation, sleep problems, and quality of life in patients with cancer. We collected demographic and clinical information using a structured survey. We assessed marital adjustment, quality of life, psychological distress profile, and sleep problems of participants using validated instruments: the Locke and Wallace Marital Adjustment Test (LWMAT), the Short-Form Health Survey-12, the Beck’s Depression Inventory (BDI), the Beck Anxiety Inventory (BAI), and the Insomnia Severity Index (ISI). Suicidal ideation was assessed with item nine of the BDI. Of the 130 patients (52.3% females, mean age 57.9 ± 12.4 years) enrolled, 20 (15%) were classified as experiencing poor marital adjustment. Moderate to severe depression, anxiety, and insomnia were found in 25.4%, 34.6%, and 24.7% of participants, respectively. Positive suicidal ideation was documented in 13.8% of participants. We found a significant association between poor marital adjustment and depression, anxiety, suicidal ideation, and poor sleep. Our study confirms the relevance of marital adjustment in relation to the psychological wellbeing of patients with cancer. Depression, anxiety, and poor sleep were found to be significantly associated with poor marital adjustment.