OBJECTIVES: The use of electronic patient reported outcomes (ePRO) within clinical trials has grown rapidly with the increasing acknowledgement by regulatory authorities that ePRO is an acceptable method and one that directly addresses many of the limitations of paper PROs. METHODS: A study of the characteristics of ePRO use in clinical drug trials was undertaken to understand the breath of therapeutic areas in which ePRO is being used as well as to understand the dimensions affecting compliance with ePRO. A dataset of 136 clinical trials was analyzed by using fields that describe each protocol’s key elements including ePRO instrument, Phase, Therapeutic Area, Disorder and mean and median compliance broken down by age deciles. RESULTS: The analysis determined that CNS (56 studies) and gastrointestinal disorders (21) represented 42% and 15% of ePRO use by the biopharmaceutical industry for this dataset. Within CNS, ePRO was used heavily in depression (24.3%), insomnia (9.6%) and anxiety protocols (8.1%). Overall, ePRO was used in 16 different major disorders and therapeutic areas. 57% of the time a named PRO instrument is used electronically; the balance of the instruments is diaries or symptom questionnaires which may not have undergone formal validation.  A sub-analysis of 8 pain studies representing 6% of the studies showed that, with one exception, patients 46 years of age and older are significantly (means of 81.6% vs. 72.5%) more compliant than study subjects younger than 46 years. The median compliance for patients 66 of age and older was 87%. CONCLUSIONS: This research shows that ePRO use within clinical trials is both broad and deep; that patients can be highly compliant; and that elderly patients are more compliant. Limitations of this study include the clinical trials of this dataset which can not be necessarily generalized as representative of all ePRO use.