Two patients, a boy aged 19 years and a girl aged 16 years, were diagnosed to be suffering from a posttraumatic stress disorder (PTSD) 7 and 2 years after sexual abuse, respectively. There was thus a serious delay in the correct diagnosis and the start of cognitive behavioural therapy, which was successful. A thorough diagnostic procedure with a semi-structured clinical interview ('Clinician administered PTSD scale') is helpful in preventing such a diagnostic delay. The omission of a structured diagnostic interview can lead to serious misjudgement. Cognitive behavioural therapy with repeated imaginary exposure to the traumatic event(s) or cognitive interventions to maladaptive beliefs is the standard treatment for PTSD in adults. Adolescents with PTSD after sexual abuse achieve a good outcome on cognitive behavioural therapy as well.