The purpose of this study was to investigate whether head-mounted displays (HMDs) change the sidetone to an auditory perceivable extent. Impulse responses (IRs) were recorded using a dummy head wearing a HMD (IRtest) and compared to IRs measured without HMD (IRref). Ten naive listeners were tested on their ability to discriminate between the IRtest and IRref using convolved speech signals. The spectral analysis showed that the HMDs decreased the spectral energy of the sidetone around 2000-4500 Hz. Most listeners were able to discriminate between the IRs. It is concluded that HMDs change the sidetone to a small but perceivable extent.