BackgroundRegistration of interventional studies is necessary according to the Declaration of Helsinki but implementation has been a challenge for many journals. Acta Anaesthesiologica Scandinavica (Acta) requires registration for studies conducted after January 1st 2010. We aimed to assess the proportion of correctly registered randomized controlled trials (RCTs) published in Acta from 2009 to 2014.MethodsWe manually searched all Acta issues from 2009 to 2014 for RCTs. Information about timing of data collection and registration in trial registries was extracted. We classified RCTs as correctly registered when it could be verified that patient enrolment was started after registration in a trial registry.ResultsWe identified 200 RCTs. Dates for patient enrolment were not specified in 51 (25.5%). The proportion of correctly registered trials increased significantly from 17.1% (19/111) for trials starting enrolment before 2010 to 63.2% after 2010 (24/38, P < 0.01). Most clinical trials were registered at clinicaltrials.gov.ConclusionMany published randomized controlled trials from Acta Anaesthesiologica Scandinavica were not adequately registered but the requirement of trial registration has resulted in a significant increase in the proportion of correctly registered trials.