BACKGROUND Clinical Learning through Extended Immersion in Medical Simulation (CLEIMS) is a new methodology for medical student learning, first reported at last year's conference. It involves students working in teams of 4-5 through the clinical progress of one or more patients over a week, utilising a range of simulation methodologies to enhance learning in associated workshops and seminars. A randomised educational trial comparing the methodology to seminars and workshops alone began in 2010. PURPOSE To report primary endpoint outcomes of the trial. METHODS 80 medical students volunteered to participate, of whom 44 were randomised to the intervention arm and 36 to the control arm. Participants undertook one week of the program in Year 3 in 2010 and will undertake a second week, focusing on the care of an Indigenous family, in Year 4 in 2011. They completed study-specific assessment at the end of each rotation as well as summative assessment at the end of each year. RESULTS No significant difference was seen between the study arms in multiple choice and script concordance questions on workshop content but intervention arm participants scored better in a prescribing exercise (mean score 67.9 vs 63.1, P= 0.02) and a resuscitation practical test (mean time-to-defibrillation 87 seconds vs 130 seconds, P=0.007) at the end of the first CLEIMS week. There were no significant between-arm differences in summative assessment marks, which avoided the stopping rule allowing the trial to continue into the second year. DISCUSSION Significant between-arm differences were seen in some primary endpoints but no significant differences in summative marks have been seen so far. Final primary endpoint outcomes will be presented at the conference. CONCLUSIONS The CLEIMS methodology appears to enhance some aspects of student learning.