Malnutrition and underweight status pose an unfavorable prognosis for cancer patients. Several studies have addressed the impact of a low body mass index (BMI) (<18.5 kg/m(2)) on ovarian cancer progression. However, their results seem to be conflicting. The present meta-analysis investigates whether the underweight status negatively affects the progress of ovarian cancer. We conducted a systematic review searching the Medline (1966-2014), Scopus (2004-2014), Popline (1974-2014), ClinicalTrials.gov (2008-2014), and Cochrane Central Register of Controlled Trials (CENTRAL) (1999-2014) databases together with reference lists from included studies. All prospective and retrospective observational cohort studies were included. Statistical meta-analysis was performed using the RevMan 5.1 software. Current evidence suggests that the stage of the disease does not differ between underweight and normal-weight patients [odds ratio (OR) 0.80, 95% confidence interval (CI) 0.46-1.39 for stage I; OR 1.27, 95% CI 0.71-2.27 for stage II; OR 1.03, 95% CI 0.71-1.51 for stage III; and OR 1.05, 95% CI 0.63-1.76 for stage IV disease]. Concurrently, the risk of residual disease after surgery (OR 1.03, 95% CI 0.69-1.52) and the risk of dying due to ovarian cancer (OR 1.08, 95% CI 0.64-1.85) seem to be similar. According to the findings of our systematic review, the underweight status does not seem to have a detrimental impact on ovarian cancer prognosis. However, the methodological limitations of published studies and the small number of enrolled underweight patients preclude firm results. Thus, future research in this field is necessary.