Objectives Diagnoses-specific sickness certification guidelines were recently introduced in Sweden. The aim of this study was to investigate to which extent general practitioners (GPs) used these guidelines and how useful they found them, 1 year after introduction. Design A cross-sectional questionnaire study. A comprehensive questionnaire about sickness certification practices in 2008 was sent to all physicians living and working in Sweden (n=36 898, response rate 60.6%). In all, 19.7% (n=4394) of the responders worked as GPs. Setting Primary healthcare in all Sweden. Participants The participating GPs who had consultations concerning sickness certification at least a few times a year (n=4278, 97%). Main outcome measures Descriptive statistics and prevalence ratios for the 11 questionnaire items about the use and usefulness of the sickness certification guidelines. Results A majority (76.2%) of the GPs reported that they used the guidelines. In addition, 65.4% and 43.5% of those GPs reported that the guidelines had facilitated their contacts with patients and social insurance officers, respectively. The guidelines also helped nearly one-third (31.5%) of the GPs to develop their competence and improve the quality of their management of sickness certification consultations (33.5%). About half experienced some problems when using the guidelines and 43.7% wanted better competence in using them. A larger proportion of non-specialists and of GPs with fewer sickness certification consultations had benefitted from the guidelines. Conclusions The national sickness certification guidelines implemented in Sweden were widely used by GPs already a year after introduction. Also, the GPs consider the guidelines useful in several respects, for example, in patient contacts and for competence development.