A supplemental oxygen delivery system is described in which Aerosol is delivered into a housing 10, 20, which sits in the circuit from the supplemental oxygen supply and optional humidifier. The supplemental oxygen passes through this chamber 10, 20 in which the aerosol is located, and collects the aerosol transporting it to a patient via a nasal cannula 3 or a face mask 4. An aerosol generator 9 is mounted to the housing 10, 20 and delivers aerosol into an oxygen stream 13 flowing between an inlet 14 and an outlet 15 of the housing 10. The housing 10 also has a removable plug 16 in the base 17 thereof for draining any liquid that accumulates in the housing 10. There is no disruption of oxygen delivery to patients using nasal cannulas who currently have to use a separate face-mask when receiving nebulized medication.