OBJECTIVE: Despite high prevalence of irritable bowel syndrome (IBS) and its significant negative impact on individuals' quality of life, its etiology remains poorly understood. This prospective study explored whether early life factors (adverse childhood experiences; ACEs) and alexithymia intensity, could explain IBS symptom severity and its effects on psychological functioning over time. We also compared the studied variables between an IBS sample and a healthy control group. METHOD: Based on the Rome III Diagnostic Criteria for IBS, 245 individuals with a diagnosis of IBS were recruited from a national sample of Poles. The IBS sample completed the following psychometric questionaries in three waves, one month apart: Adverse Childhood Experiences Questionnaire, Toronto Alexithymia Scale, IBS Symptom Severity Score, Short Form Perceived Stress Scale, and Ultra-Brief Patient Health Questionnaire for Anxiety and Depression. Latent transition analysis was used to identify distinct profiles of IBS symptom dynamics. RESULTS: The IBS group reported a significantly higher number of ACEs, greater alexithymia severity, and more intense levels of stress, anxiety, and depressive symptoms compared to the healthy controls. Four profiles of IBS individuals with distinct dynamics of IBS symptoms, stress, anxiety, and depressive symptoms were extracted, which correlated with the baseline number of ACEs and alexithymia intensity among participants. CONCLUSION: Childhood adversity and associated problems in emotional processing affect IBS symptom severity. ACEs should be included in IBS screening and considered in the design of individualized multidisciplinary treatment approaches for IBS patients.