The 2009 pandemic of novel swine-origin influenza A (H1N1) highlighted the importance of community mitigation measures such as voluntary isolation. During the pandemic, we investigated the voluntary isolation behavior of patients with influenza during the 7-day period after they visited an outpatient clinic at a hospital in Tokyo, Japan. A questionnaire-based survey was conducted on patients diagnosed with influenza. Of a total of 14 patients, 13 (93%) visited a workplace, school or other potentially crowded setting at least once in the 7-day period after presentation. Five patients (36%) visited a potentially crowded setting either with a fever or on the day after having a fever. The voluntary isolation behavior of Japanese people with influenza did not necessarily adhere to the Japanese government recommendation that people with influenza-like illness stay home for 7 days following the onset of symptoms.