Marital satisfaction, which is typically assessed with multi-item measures, has been linked to health benefits among both civilian and military samples. Despite some advantages over multiple-item measures, researchers are less likely to use single-item marital satisfaction measures perhaps because there are few studies that demonstrate their reliability and validity. This study provided validation evidence, reliability estimates and replicated the cut-off of the Brief Marital Screening Tool (SI measure) in three military-affiliated samples (two of service members [N = 850 and N = 936] and one military spouse sample [N = 333]). Analyses showed that the SI measure had acceptable reliability using two estimation techniques. Further, in comparison with the multi-item measures, the SI measure showed similar associations with mental health, physical health, and relationship functioning outcomes establishing the SI measure’s criterion validity. Lastly, findings also confirmed the cut-off established in the original validation paper using two different multiple-item marital satisfaction measures. The implications of the findings for research, interventions, and clinical practice are discussed.