Do doctor-related factors influence the duration of episodes of sickness certification? This problem was studied in an analysis of 2,999 persons certified sick by 107 general practitioners in Buskerud county, Norway, during a 4-week period in 1985. Doctors' attitudes toward sickness certification were measured by composing an index based on 12 statements (Likert scale), "weighed" by principal component analysis. Doctors' sickness certification practice was measured by duration of each episode of sickness certification. The analysis revealed no association between doctors' attitudes toward sickness certification and the duration of the episodes. Cox regression analysis showed, however, that the duration was significantly longer in patients of the oldest doctors, while it was shorter in patients of specialists in general practice and of GPs working part-time as industrial medical officers.