Numerous technical, cognitive, interpersonal and personal characteristics are important for effective outdoor adventure leadership. The purpose of this study was to identify and compare measurable characteristics of highly effective and ineffective outdoor leaders. The Adjective Check List (ACL) was selected for identifying personal and interpersonal characteristics or attributes. It consists of 300 adjectives and adjectival phrases commonly used to describe a person’s attributes, and can be administered to an individual to elicit a self-evaluation. Seven outdoor adventure programs with excellent national reputations were identified and selected to participate in the study. Selection was based upon a program having a national reputation for excellence over at least a ten-year period. Program directors were contacted via telephone and asked to participate. Written instructions were mailed to each program director asking them to select one to three leaders they believed to be “highly effective outdoor adventure leaders” and who they would want to retain for their staff. In addition, they were instructed to select one to three leaders they believed to be “poor or ineffective outdoor adventure leaders” and whom they would not rehire. The selected leaders were given a copy of the ACL and asked to complete and return it to the researcher in a self-addressed post-paid envelope. The leaders were not told why they were selected, just that they had been asked to participate in a research project regarding outdoor adventure leaders. The instruments were coded, so the research team could distinguish between those identified as effective and ineffective. Completed ACLs were received from eight program directors, with 19 leaders identified as “highly effective”, and 10 as “ineffective”. ACLs were scored, and raw scores for 37 characteristics were converted to t-scores. The 37 t-scores were analyzed by two-way ANOVA (effective vs. ineffective and male vs. female) for the 37 characteristics. Multivariate analysis was inappropriate due to unequal cell sizes and insufficient degrees of freedom. Results indicated nine characteristics showing statistically significant differences between effective and ineffective leaders, and eight characteristics indicating differences between genders. These data provide valuable professional development information for current outdoor leaders, as well as future leaders and their instructors. Keyword(s): leadership development, outdoor ed/recreation, research