Introduction: First episode-psychosis (FEP) represents a stressful/traumatic event for patients. To our knowledge, no study to date has investigated thought suppression involved in FEP in a Romanian population. Our objective was to investigate thought suppression occurring during FEP within primary psychotic disorders (PPD) and substance/medication induced psychotic disorders (SMIPD). Further, we examined the relationship between thought suppression and negative automatic thoughts within PPD and SMIPD. Methods: The study included 30 participants (17 females) with PPD and 25 participants (10 females) with SMIPD. Psychological scales were administered to assess psychotic symptoms and negative automatic thoughts, along a psychiatric clinical interview and a biochemical drug test. Results: Participants in the PPD group reported higher thought suppression compared to SMIPD group. For the PPD group, results showed a positive correlation between thought suppression and automatic thoughts. For the SMIPD group, results also showed a positive correlation between thought suppression and automatic thoughts. Conclusions: Patients with PPD rely more on thought suppression, as opposed to SMIPD patients. Thought suppression may be viewed as an unhealthy reaction to FEP, which is associated with the experience of negative automatic thoughts and might be especially problematic in patients with PPD. Cognitive behavioral therapy is recommended to decrease thought suppression and improve patients’ functioning.