Objectives: To compare and contrast the geographic and demographic distribution of bro β-lactamase and antibiotic MIC50/90 for 1440 global Moraxella catarrhalis isolates obtained from children and adults between 2001 and 2002. Methods: One thousand four hundred and forty M. catarrhalis isolates originating from seven world regions were investigated. The isolates were recovered from 411 children <5 years of age and 1029 adults >20 years of age. PCR-restriction fragment length polymorphism (RFLP) was performed to determine bro prevalence and to distinguish between bro types. MIC values of 12 different antibiotics were determined using the CLSI (formerly NCCLS) broth microdilution method. Results: Of the 1440 isolates, 1313 (91%) possessed the bro-1 gene and 64 (4%) possessed the bro-2 gene. Additionally, the prevalence of bro positivity between the child and adult age groups was significantly different (P<0.0001), though bro-1 and bro-2 prevalences within age groups were not significantly different. Consistently higher β-lactam MICs were observed for M. catarrhalis isolates originating in the Far East. Significant correlations in MICs were observed for several antibiotic combinations, including all five β-lactams with each other, and among the two quinolones. Conclusions: The worldwide prevalence of bro gene carriage in clinical isolates of M. catarrhalis is now approaching 95%, with children significantly more likely to harbour bro-positive isolates than adults. Further, statistically significant differences in the distribution of β-lactam MICs were observed between different world regions, particularly with respect to the Far East.