Purpose: The Department of Pediatrics at SUNY Upstate Medical University in collaboration with the Instructional Design, Development, and Evaluation Department in Syracuse University's School of Education recently undertook a curricular reform effort that included translation of the residency program's annual core didactic lecture series to an online format. The present study examines the design factors and pedagogical techniques that enhanced or inhibited the successful implementation of the newly developed online core curriculum. Methods: This study employed a qualitative focus group methodology to identify learner perceptions of the affordances and barriers of the Pediatric Online Core Curriculum for resident education. Four focus group sessions were conducted with a mixture of 1st, 2nd and 3rd year residents participating in the pediatric residency program at SUNY Upstate Medical University. Anonymous transcripts of the interview sessions were independently coded and utilized in the data analysis. Results: Eight major themes emerged that impacted the learning experience of residents utilizing the online curriculum. These themes included; curriculum quality, design, feedback, implementation, media features, integration, time, and learner centered issues. The study analysis concludes with six design principles for online curricula to promote their successful employment and utilization. Conclusions: The potential benefits of online learning systems will not be realized unless appropriate instructional methods are employed in their design and development. The present study examines the perceived affordances and barriers to implementation of online curricula and concludes with principles that can be used to influence the design of future curricula. (Contains 2 figures.)