The assumption that participants receiving an ICD10 diagnosis of posttraumatic stress disorder (PTSD) will also receive a DSM-IV diagnosis of PTSD was tested. Data were gathered for 1,364 participants using the Composite International Diagnostic Interview (CIDI). The 12-month prevalence of PTSD was 3% for DSM-IV and 7% for ICD10 Diagnostic Criteria for Research (ICD10-DCR). The agreement between the two systems was fair (kappa = .50). Forty eight percent of the discrepancies between the systems were accounted for by the additional criterion requiring clinically significant distress or impairment included in DSM-IV. The inclusion of symptoms of general numbing of responsiveness accounted for 18% of the discrepancies. It is concluded that ICD10-DCR PTSD cannot be assumed to be identical to DSM-IV PTSD.