Cancer patients are particularly vulnerable to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and have a poor prognosis if they develop coronavirus disease (COVID-19). Nosocomial infection is of particular concern in patients with multiple myeloma (MM). Here, we analyzed the clinical course of nine patients with MM admitted for chemotherapy in our hospital who developed nosocomial COVID-19. Of the 4 patients who survived, 2 patients (before starting or soon after the interruption of induction therapies) did not develop severe COVID-19 symptoms, such as respiratory failure. The other 2 patients were in “very good partial remission” at the time of disease development. All patients who survived acquired anti-SARS-CoV-2 antibodies. The remaining 5 patients died due to acute respiratory distress syndrome, with a median survival of 10 days from symptom onset or a positive result for viral RNA. All patients who died had a status poorer than “very good partial remission” status while receiving anti-myeloma chemotherapy. MM patients may be at greater risk of unfavorable COVID-19 outcomes, especially if they have not attained a sufficient treatment response or are immunosuppressed following viral infection.