A long duration of computer use is known to be positively associated with Work Related Upper Extremity Disorders (WRUED). Self-report by questionnaire is commonly used to assess a worker's duration of computer use. The aim of the present study was to assess the validity of self-report and computer use software (WorkPace®) to assess the duration of computer use in a heterogeneous office population and for different job types. Ninety-nine bank employees with various job titles participated in the study. The duration of computer use was assessed simultaneously by self-report (questionnaire), WorkPace® and direct observation. Observation was regarded as the golden standard. On average, self-reports overestimated the observed duration of computer use with 39%. This overestimation was reduced to 9% when using WorkPace®. Viewing times (time viewing the screen without touching mouse or keyboard) differed between computer jobs. It was concluded that computer use statistics yield rather accurate estimations of duration of computer use, whereas self-reports do not. These estimations can be further improved by using specific viewing time estimations for different computer jobs. Relevance to industry: To develop guidelines for safe duration of computer use and to assess high-risk groups, valid but simple exposure assessment methods are needed. Computer use software proves to be more valid than self-reports by questionnaire that are commonly used. © 2007 Elsevier B.V. All rights reserved.