Although influenza may be propagated in innumerable occasions and daily situations involving exposure, basketball may create many chances for close contact in which influenza could spread. This study aims to quantify and assess the impact of the 2009 H1N1 influenza pandemic among professional basketball players. A multi-step strategy was followed to gather the relevant data during the 2009-10 basketball season. Possible risk factors were recorded; logistic regression was performed to assess the impact of the former. Where data were only available in the press, cases were also verified by subsequent communication with the national basketball federations. Relevant data were available for 18 countries (218 teams, 3,024 players). In all, 52 H1N1 cases in 19 teams were reported. A larger number of players presented as a risk factor for the emergence of H1N1 cases to a borderline extent (Odds Ratio, OR 1.19, 95% CI 1.00-1.41, p 0.056). A borderline association also implicated the population of the city-basis (OR 1.01, 95% CI 1.00-1.02, p 0.094). On the other hand, no significant association with risk of H1N1 emergence was demonstrated regarding latitude and longitude of the city-basis. Even in environments where the best possible preventive and other medical care is provided influenza continues to be a threat. The microenvironment (crowding index, players per team) seemed to represent the most meaningful predictor regarding H1N1 emergence in a basketball team.