We aimed to characterize incident users of alendronate from Denmark and Spain, and investigate their eligibility for participation in the pivotal Fracture Intervention Trial (FIT). This is an international cross-sectional study, where the data were obtained from the SIDIAP database (Sistema d'Informació per al Desenvolupament de l'Investigació en Atenció Primària) from Catalonia (Spain) and the Danish Health Registries (DHR). This study included patients who were incident users of alendronate, ≥40 years old with no history of Paget's disease. Our measurements were the proportion of incident users of alendronate who were not eligible to participate in FIT. 14,316 and 21,221 subjects initiated alendronate in 2006-2007 (SIDIAP) and 2005-2006 (DHR), respectively. SIDIAP and DHR alendronate user cohorts had 2347 (16.4 %) and 5275 (24.9 %) subjects aged >80 years old, reported 9 (0.1 %) and 91 (0.4 %) diagnoses of myocardial infarction, 423 (3 %) and 368 (1.7 %) of erosive gastro-intestinal disease, 200 (1.4 %) and 1109 (5.2 %) of dyspepsia, and 349 (2.4 %) and 149 (0.7 %) of metabolic bone disease, all of which were exclusion criteria in FIT. Men [3818 (26.7 %) in SIDIAP and 3885 (18.3 %) in DHR] and glucocorticoid users [1229 (8.6 %) in SIDIAP and 4716 (22.2 %) in DHR] were also excluded from the FIT trial. Overall, 3447 (35.4 %) SIDIAP and 6228 (44.5 %) (when not considering men and glucocorticoid users) DHR of incident alendronate users would have been excluded from FIT. One in two real-life users of alendronate exhibited one or more clinical characteristics that would have led to them being excluded from the FIT trial.