OBJECTIVES:  To explore the feasibility and utility of using social media-based patient networks to gather qualitative data on patient reported outcome (PRO) concepts relevant to Chronic Lymphocytic Leukemia (CLL). METHODS:  Adults with CLL participating as members of the PatientsLikeMe online patient community were invited to complete a web-based survey about their experiences with the condition.  Open-ended survey questions elicited descriptions of CLL symptoms, impacts, and treatment-related perceptions.  Other questions included CLL stage and treatment status, performance status, and demographic characteristics.  Survey responses and interview transcripts were coded for qualitative content analysis using Atlas.ti. RESULTS:  Survey responses from 50 members of the PatientsLikeMe CLL community were coded for content analysis.  The mean age of respondents was 60.5 years, 54.0% were female, and 96% were White. When surveyed, 20% of respondents were receiving current treatment.  Among those not receiving treatment, the majority (77.5%) were treatment naïve, while another 20% were in remission. The majority of patients (78.0%) reported experiencing at least 1 symptom and 17% of patients reported their symptoms required them to be in bed for up to 50% of their waking day. Among  50 patients, 369 descriptions of CLL symptoms were coded.  Fatigue was the most frequently-expressed symptom (described by 40% of respondents), followed by tiredness (38%), night sweats (38%), swollen lymph nodes (32%), and frequent infections (28%).  Among impacts of CLL, worry and fear (66% of respondents), depressed feelings (52%), and work limitations (50%) were noted most frequently. CONCLUSIONS: Survey results identified constitutional symptoms of CLL included in existing PRO instruments and the literature. These findings suggest that qualitative data obtained through social media applications can be potentially useful in supporting concept identification for newly-developed PRO instruments.  Further research is needed to identify whether the results can support content validity in the same way as established qualitative research methods.