The invention relates to a method of and device for monitoring a vital parameter of a patient by emitting light onto tissue of the patient with at least one light source (1, 2) and collecting light which is transmitted through the tissue and/or which is reflected from the tissue. The emitted light is multiplexed according to a predefined multiplexing scheme having a plurality of multiplexing channels, and the collected light is detected according to the predefined multiplexing scheme, resulting in a plurality of detection channels (16, 17, 18, 19). At least one of the multiplexing channels is arranged to be a dark multiplexing channel for which no light is emitted by the at least one light source (1, 2), resulting in a dark detection channel (19), and the signal of this dark detection channel (19) is used for generating a reference signal for reducing interference in the signal of at least one of the other detection channels (16, 17, 18). In this way a versatile and reliable possibility of monitoring a vital parameter of a patient with a high signal-to-interference ratio is provided.
