Background: In the choice and definition of quality of care indicators, there may be an inherent tension between feasibility, generally enhanced by simplicity, and validity, generally enhanced by accounting for clinical complexity. Objectives: To study the process of developing quality indicators using an expert panel and analyze the tension between feasibility and validity. Design and participants: A multidisciplinary panel of 12 expert physicians was engaged in two rounds of modified Delphi process to refine and choose a smaller subset from 36 indicators; these were developed by a research team studying the quality of care in ambulatory post-myocardial infarction patients with co-morbidities. We studied the correlation between validity/feasibility ranks provided by the expert panel. The correlation between the quality indicators ranks on validity and feasibility scale and variance of experts' responses was also individually studied. Results: Ten of 36 indicators were ranked in both the highest validity and feasibility groups. The strength of association between validity and feasibility of indicators measured by Kendall tau-b was 0.65. In terms of validity, a strong negative correlation was observed between the ranks of indicators and the variability in expert panel responses (Spearman's rho, r = -0.85). A weak correlation was found between the ranks of feasibility and the variability of expert panel responses (Spearman's rho, r = 0.23). Conclusion: There was an unexpectedly strong association between the validity and feasibility of quality indicators, with a high level of consensus among experts regarding both feasibility and validity for indicators rated highly on each of these attributes. © The Author 2010. Published by Oxford University Press in association with the International Society for Quality in Health Care; all rights reserved.