The paper presents the results of a longitudinal study of two groups of participants of motor vehicle accidents (MVA). They were investigated twice: The first time after 1–6 months (N = 362) or 12–24 months (N = 337) after a MVA, and then 1 year after the initial assessment. We assumed that, among the environmental variables (severity of experienced trauma, trauma-related prolonged stressors, other traumatic event and social support), two temperamental traits, emotional reactivity and briskness, would be factors influencing the severity of posttraumatic stress disorder.