Disclosed is a size-adjustable headset for monitoring bioelectrical signals, the headset comprising: a headband configured to be put on a user's head, wherein the headband comprises a first connector element; at least one side band comprising a second connector element distant from a first end of the at least one side band; and at least one electrode contact configured to be electrically connected to a measurement electrode, wherein the first connector element and the second connector element are configured to be connected to one another such that a length of the at least one side band between the first end and the first connector element can be adjusted. Further disclosed is an EEG measurement system comprising the headset and an EEG measurement electrode.