We present a climatology of mid-latitude cirrus cloud properties based on 13 000 hours of automatically analyzed lidar measurements at three different sites. Jungfraujoch, situated at 3580 m a.s.l., is found to be ideal to measure high and optically thin cirrus. We use our retrieved optical properties together with a radiation model and estimate the radiative forcing by mid-latitude cirrus. All cirrus clouds detected here have a positive net radiative effect.