Existing validated measures of pharmacist-physician collaboration focus on measuring attitudes toward collaboration and do not measure frequency of interactions that comprise actual collaborative behavior. Therefore, the aim of this study was to develop and validate an instrument to measure the frequency of collaboration between general practitioners (GPs) and pharmacists from the GP's perspective. An 11-item Frequency of Interprofessional Collaboration Instrument for GPs (FICI-GP) was developed and administered to 1118 GPs in eight divisions of general practice in New South Wales, Australia. Two hundred and fifty-eight (23%) GP surveys were completed and returned. Principal component analysis suggested removal of one item for a final one-factor solution. The refined 10-item FICI-GP had a Cronbach's alpha of 0.87. After collapsing the original five-point response scale to a three-point response scale, the refined FICI-GP demonstrated fit to the Rasch model. Criterion validity of the FICI-GP was supported by the correlation of FICI-GP scores with scores on a previously validated physician-pharmacist collaboration instrument as well as by predicted differences in FICI-GP scores between subgroups of respondents stratified on age, co-location with pharmacists and interactions during residency. The refined 10-item FICI-GP was shown to have good internal consistency, criterion validity and fit to the Rasch model.