BACKGROUND: Metabolic syndrome (MetS) and posttraumatic stress disorder (PTSD) often co-occur and both may compromise cognition, owing in part to common underlying mechanisms. Few studies have investigated the additive effects of these disorders on cognitive performance. Our aims were to compare cognitive performance between patients with PTSD and trauma-exposed controls (TEC) and investigate the additive effects of MetS factors on cognition. METHODS: In this case-control study, we included 474 adult participants, 236 with PTSD and 238 TEC. Demographic, neuropsychiatric, metabolic-related, and neurocognitive assessments were undertaken and MANCOVAs performed controlling for age. Cognitive domains (immediate and delayed memory, attention, language, visuospatial performance, working memory and global cognition) were the dependent variables in the analysis. Patient status and presence/absence of MetS or MetS components were independent variables, in each model. RESULTS: Patients with PTSD did not demonstrate worse cognitive performance than TEC on the neurocognitive domains assessed, and the presence of MetS in patients with PTSD did not alter this finding. Individuals with MetS also did not demonstrate worse cognition when compared to those without MetS. When we looked at individual MetS features, higher BMI was associated with poorer visuospatial performance, CONCLUSIONS: These findings contrast with many previous studies showing worse neurocognitive performance related to both PTSD and MetS. Further investigation is required to establish the contribution of MetS to cognitive deficits in those with PTSD. Generalisability and inferences regarding the directionality of associations are limited.