BACKGROUND: The importance of effective team leadership for achieving surgical excellence is widely accepted, but we understand less about the behaviors that achieve this goal. We studied cardiac surgical teams to identify leadership behaviors that best support surgical teamwork. METHODS: We observed, surveyed, and interviewed cardiac surgical teams, including 7 surgeons and 116 team members, from September 2013 to April 2015. We documented 1,926 surgeon/team member interactions during 22 cases, coded them by behavior type and valence (ie, positive/negative/neutral), and characterized them by leadership function (conductor, elucidator, delegator, engagement facilitator, tone setter, being human, and safe space maker) to create a novel framework of surgical leadership derived from direct observation. We surveyed nonsurgeon team members about their perceptions of individual surgeon's leadership effectiveness on a 7-point Likert scale and correlated survey measures with individual surgeon profiles created by calculating percentage of behavior types, leader functions, and valence. RESULTS: Surgeon leadership was rated by nonsurgeons from 4.2 to 6.2 (mean, 5.4). Among the 33 types of behaviors observed, most interactions constituted elucidating (24%) and tone setting (20%). Overall, 66% of interactions (range, 43%-84%) were positive and 11% (range, 1%-45%) were negative. The percentage of positive and negative behaviors correlated strongly (r = 0.85 for positive and r = 0.75 for negative, p < 0.05) with nonsurgeon evaluations of leadership. Facilitating engagement related most positively (r = 0.80; p = 0.03), and negative forms of elucidating, ie, criticism, related most negatively (r = -0.81; p = 0.03). CONCLUSIONS: We identified 7 surgeon leadership functions and related behaviors that impact perceptions of leadership. These observations suggest actionable opportunities to improve team leadership behavior.