The purpose of the study was to document development costs and estimate implementation costs of an Internet-based medication adherence intervention for people living with HIV in the United States. Participants (n = 61) were enrolled in the 8-week study in 2011 and entered the intervention website remotely in the setting of their choice. Development costs were obtained from a feasibility and acceptability study of an Internet-based medication adherence intervention. Implementation costs were estimated based on an 8-week trial period during the feasibility and acceptability study. Results indicated that although developing an Internet-based medication adherence intervention is expensive, the monthly cost of implementing and delivering the intervention is low. If the efficacy of similar interventions can be established, these results suggest that Internet could be an effective method for delivering medication adherence interventions to persons residing in areas with limited access to in-person adherence services.