The invention relates to a wind turbine comprising a system for monitoring at least one wind turbine component including a closed fluid circulating system with a fluid reservoir. The monitoring system comprises, means for establishing a level value of the fluid systems reservoir, and means for establishing at least one environmental value of the fluid systems reservoir or the surroundings of the system. The level value and the at least one environmental value contributing to defining the fluid systems functionality, and the monitoring system further comprises means for establishing a monitoring value on the basis of the level value and the at least one environmental value. The invention further relates to a method for monitoring at least one wind turbine component including a closed fluid circulating system with a fluid reservoir and a system for monitoring a mechanical and/or electrical component.