Posttraumatic stress disorder (PTSD) is a prevalent psychiatric condition that significantly increases the risk of suicide. This study aimed to assess PTSD and its co-occurring conditions among individuals who attempted suicide and to evaluate the relationship between these disorders and suicide reattempts within six months. This prospective cohort study included 2,441 individuals from the French Vigilans programme who attempted suicide between 2015 and 2020. Data on sociodemographic characteristics and suicide attempt (SA) history were collected at baseline, and lifetime psychiatric conditions were assessed via the Mini-International Neuropsychiatric Interview (MINI) during the six-month follow-up telephone interview. Multivariate logistic and linear regression models were used to measure the impact of PTSD and its comorbidities on suicide reattempts within six months, controlling for sex, age, and prior SAs. In total, 11.8% of the individuals (287/2,441) in the cohort were diagnosed with PTSD. Among these, 71.1% (204/287) had major depressive disorder, 36.2% (104/287) had alcohol use disorder, and 35.9% (103/287) had panic disorder. Within six months, we observed higher rates of suicide reattempt in those with PTSD (< .01; 1.71 95% CI 1.14-2.55), regardless of comorbidities. Even higher rates were found in those with PTSD comorbid with panic disorder (= .02 1.95 95% CI 1.12-3.39) or substance use disorder (= .01 2.91 95% CI 1.28-6.62). Additionally, PTSD comorbid with panic disorder (= .02, = .10) or eating disorders (= .04, = .12) was associated with a greater number of suicide reattempts. Approximately one in ten SA survivors experienced PTSD. Individuals with PTSD and comorbid conditions, such as panic disorder, substance use disorder, and eating disorders, are two to three times more likely to reattempt suicide within six months. Despite ongoing preventive efforts, rates of reattempt remain high, highlighting the urgent need for continuous clinical monitoring and personalized therapeutic interventions. ClinicalTrials.gov identifier: NCT03134885.