['Patient portals may improve pediatric chronic disease outcomes, but few have been rigorously evaluated for usability by parents. Using scenario-based testing with think-aloud protocols, we evaluated the usability of portals for parents of children with cystic fibrosis, diabetes or arthritis. DESIGN Sixteen parents used a prototype and test data to complete 14 tasks followed by a validated satisfaction questionnaire. Three iterations of the prototype were used.', 'During the usability testing, we measured the time it took participants to complete or give up on each task. Sessions were videotaped and content-analyzed for common themes. Following testing, participants completed the Computer Usability Satisfaction Questionnaire which measured their opinions on the efficiency of the system, its ease of use, and the likeability of the system interface. A 7-point Likert scale was used, with seven indicating the highest possible satisfaction.', 'Mean task completion times ranged from 73 (+/- 61) seconds to locate a document to 431 (+/- 286) seconds to graph laboratory results. Tasks such as graphing, location of data, requesting access, and data interpretation were challenging. Satisfaction was greatest for interface pleasantness (5.9 +/- 0.7) and likeability (5.8 +/- 0.6) and lowest for error messages (2.3 +/- 1.2) and clarity of information (4.2 +/- 1.4). Overall mean satisfaction scores improved between iteration one and three.'] Does usability testing found problems for novice users of pediatric portals?