OBJECTIVES: The internet is a valuable resource for accessing health information and support. This study aimed to develop a tool (the eHIQ) to measure the impact of using health-related websites which contain experiential and factual information. METHODS: A multi-method study with four stages. Stage 1: Themes concerning the impact of using health-related websites were identified through qualitative secondary analysis of interviews exploring patient and carer experiences of health and a relevant literature review. Stage 2: Questionnaire items based upon identified themes were constructed and assessed using expert and patient opinion. Stage 3: Items were administered online and subjected to exploratory factor analysis. Stage 4: The reduced questionnaire and appropriate reference measures were administered online to test convergent validity and external reliability. RESULTS: Sixty-seven items were constructed according to the key themes identified through relevant literature and qualitative analysis. Following expert and patient refinement, two independent item pools were entered into psychometric testing. The first item pool (eHIQ-Part 1) related to general views of using the internet in relation to health and second item pool (eHIQ-Part2) related to the impact of using a specific health-related website. Analysis confirmed three domains present in eHIQ-Part 1 and six domains present in eHIQ-Part 2. These domains were tested further during Stage 4 and were found to have high convergent validity, internal consistency and good test-retest reliability. CONCLUSIONS: Developing the eHIQ through the use of qualitative analysis and patient-expert opinion enhanced face and content validity.  The eHIQ demonstrates good psychometric properties and will enable the measurement of the effects of using health-related websites across a range conditions.