Background: The objective of this study was to find out the most important influences affecting the women's choice of a fitness club and to show that a fitness instructor is one of the significant factors in this decision making process. Comprehensive understanding by instructors of the women's decision making process will help in improving the women's satisfaction level, hence their regular participation in fitness activities.Material/Methods: Two different target groups connected with the activity of fitness clubs were studied. In the first one there were 339 female fitness class participants at the age of 13 to 76. There were 188 group fitness instructors at the age of 19 to 59 in the second target group. Both groups filled in a questionnaire constructed for this research project. 17 factors that might affect the women's choice of a fitness club were analyzed.Results: The study reveals that fitness instructors' qualifications and the factors connected with their work have a much more important impact on the women's choice of a club than some other promotional activities.Conclusions: Maintaining a high level of fitness instructors' qualifications and enabling them to deliver the highest quality of work should have the highest priority in the marketing strategy of fitness clubs. High expectations that women have of fitness instructors prove the necessity of developing training standards for leisure time physical activity instructors in Poland. This is essential to ensure an appropriate level of their professional qualifications.