Objectives: The aim of this study was to examine open-source electronic health record (EHR) software to determine their level of functionalities according to the International Organization for Standardization (ISO) standards. Methods: ISO standards were used as a guideline to determine and describe the reference architecture and functionalities of a standard electronic health record system as well the environmental context for which the software has been built. Twelve open-source EHR systems were selected and evaluated according to two-dimensional criteria based on ISO/TS 18308:2004 functional requirements and ISO/TR 20514:2005 context of the EHR system. Results: Open EHR software programs mostly fulfill structural, procedural, evolutional, and medicolegal requirements at the minimal and full functionality levels. Communication, privacy, and security requirements are accomplished in less than 23 percent of the cases, mainly at minimal functional level. Ethical, cultural, and consumer requirements still need to be fulfilled by free and open-source EHR applications. Conclusions: Most analyzed systems had several functional limitations. Nevertheless, especially for clinicians and decision makers in developing countries, open-source EHR systems are an option. The limited functionalities are likely to become requirements for further releases of open-source EHR systems.