Background Shared decision making is an important aspect of patient centredness. Lack of this consulting behaviour is a common reason for failure in the Membership of the Royal College of General Practitioners (MRCGP) consulting skills examination. Aim To investigate candidates' performance in shared decision making and overall performance in the MRCGP consulting skills assessment compared with an independently validated measure, the OPTION ('observing patient involvement') scale. Design Cross-sectional study. Setting MRCGP examination, UK. Participants Two hundred and fifty-two consultations submitted by 36 GPs submitting seven consultations per videotape. Method A stratified sample of 63 candidates, 21 each from fail, pass and merit selected from candidates in the MRCGP consulting skills examination, were approached for participation. Participants' examination videotapes were independently assessed for shared decision making using the OPTION scale by two non-clinical raters. Results Thirty-six candidates (of 63; 57%) who participated were no different from non-participants. Candidates who passed the 'sharing management options' in the MRCGP had significantly higher OPTION scores than those who did not (35.4 versus 27.3; mean difference = 8.1, P = 0.044). There was a significant difference between OPTION scores of MRCGP candidates with 'fail' and 'pass' (including pass with merit): 28.6 versus 36.1, 95% confidence interval CI = 1.13 to 13.87. Scores decreased as clinician age increased but were not significantly associated with sex of GP, age or sex of patient or consultation duration. The probability of passing the MRGCP increased as OPTION scores increased. Conclusion This study demonstrated concurrent validity of the MRCGP consulting skills assessment of sharing management options against an independent validated instrument for shared decision making, the OPTION scale. Candidates who performed best in the MRCGP exhibited high scores with OPTION. This study provides the basis for further work to demonstrate evidence for the potential of training for professional assessment to improve consulting competence. [ABSTRACT FROM AUTHOR]