Background: There is an increasing population of health information consumers (HIC) with multiple conditions (multimorbid). Previous studies explored the online behavior of HIC in general or HIC with a specific disease; however, the behavior of multimorbid HIC remains poorly researched. Objectives: This research aims to investigate the behaviors of the multimorbid HIC on community Q&A platforms. Methods: Using kidney disease, a prevalent disease with high likelihood of multimorbidity as a case, we analyzed the online interaction behaviors of HIC with multimorbidity in Quora, a community Q&A platform, and compared them to those of single-disease HIC. Results: The findings of this study reveal significant differences in the online interaction behavior between HIC of single vs. multimorbid diseases. Compared with single-disease HIC, multimorbid HIC are more active in multiple aspects, such as asking questions, following different topics or users, and providing suggestions for improvement of questions and answers. Additionally, multimorbid HIC are more likely to add topics to their questions, and their questions tend to attract more answers than those of single-disease HIC. On the other hand, questions and answers provided from single disease HIC had more views, followers, and upvotes than those from multimorbid HIC. Conclusion: The high level of activity among multimorbid HIC can be explained by their complex needs for information, driving an increased number of questions and drawing more attention from the whole community in answering them. Multimorbid HIC appear to be valuable contributors to the online community and reasons for the reduced visibility and upvoting of their answers should be investigated.