PTSD among a sample of mass-evacuated adults from Kosovo was studied using a prospective design with a baseline study and follow-ups at 3 and 6 months in Sweden, and with an additional follow-up after 1.5 years in both Sweden and Kosovo. Trauma events and PTSD-related symptoms were measured by the Harvard Trauma Questionnaire (HTQ). At the additional follow-up after 1.5 years the same measure (HTQ) was used as well as clinical diagnostic interviews with the SCID instrument and measurement of saliva cortisol levels. Thirty-seven percent had PTSD-related symptoms at baseline. Morbidity increased at the three follow-ups. About 80% of the participants had PTSD at the additional follow-up after 1.5 years. The HTQ results were confirmed by clinical diagnoses and the participants diagnosed with PTSD also had low saliva cortisol levels. The results are discussed in terms of trauma, time needed to develop PTSD, post-migration stress and selection mechanisms.