OBJECTIVE: The 12-item "observing patient involvement" (OPTION(12))-instrument is commonly used to assess the extent to which healthcare providers involve patients in health-related decision-making. The five-item version (OPTION(5)) claims to be a more efficient measure. In this study we compared the Dutch versions of the OPTION-instruments in terms of inter-rater agreement and correlation in outpatient doctor-patient consultations in various settings, to learn if we can safely switch to the shorter OPTION(5)-instrument. METHODS: Two raters coded 60 audiotaped vascular surgery and oncology patient consultations using OPTION(12) and OPTION(5). Unweighted Cohen's kappa was used to compute inter-rater agreement on item-level. The association between the total scores of the two OPTION-instruments was investigated using Pearson's correlation coefficient (r) and a Bland & Altman plot. RESULTS: After fine-tuning the OPTION-manuals, inter-rater agreement for OPTION(12) and OPTION(5) was good to excellent (kappa range 0.69-0.85 and 0.63-0.72, respectively). Mean total scores were 23.7 (OPTION(12); SD=7.8) and 39.3 (OPTION(5); SD=12.7). Correlation between the total scores was high (r=0.71; p=0.01). OPTION(5) scored systematically higher with a wider range than OPTION(12). CONCLUSION: Both OPTION-instruments had a good inter-rater agreement and correlated well. OPTION(5) seems to differentiate better between various levels of patient involvement. PRACTICAL IMPLICATION: The OPTION(5)-instrument is recommended for clinical application.