As patients become more involved in decisions affecting their health, it is important to monitor and improve the support clinicians provide to facilitate shared decision making. The Decision Support Analysis Tool (DSAT) was developed as a research tool to evaluate practitioners' use of decision support and related communication skills during a clinical encounter. The DSAT, consisting of six categories of decision support skills and four categories of communication skills, was tested with 34 actual transcripts of patient-physician dialogue. The patients were prepared for the clinical encounter with either a detailed decision aid plus worksheet (n=16) or a pamphlet (n=18). Pairs of raters, blinded to the intervention allocation, coded each transcript independently. The overall inter-rater agreement and kappa coefficients were, respectively 75% and 0.59 for the decision support skills and 76% and 0.68 for the communication skills categories. The frequency of DSAT skills coded: (a) were significantly correlated with three out of six patient and physician outcome measures (r>0.30, P<0.05); and (b) showed significant discrimination (P=0.05) or trends (P<0.15) in discrimination between the decision aid and pamphlet groups. The DSAT shows promise as a reliable and valid evaluation tool but requires further testing with larger samples.