A computational analysis of the periods and structure of surface seiches of Lake of Ztirich and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Ziirich, Ps and Rapperswil is given. After a brief historical account the governing equations and the procedure, how they were discretized by a finite element technique are introduced. Computational results concern seiche periods and seiche structure, in particular co-range and co-tidal lines for the first seven free oscillations which are discussed in detail. Experimental verification is from recordings taken during January 1982. Inspection by eye allows identification of the three lowest order seiche periods including the phase shift between the recordings of Ztirich and Rapperswil. Higher order modes (up to order 19) are also detected by this method. Power spectral analysis including interstation phase shift and coherence allow identification of over fifteen seiche periods. Agreement between the theoretically predicted and experimentally determined periods is excellent for the first, second, third, fair for the fourth, fifth and sixth mode and good for the other higher modes, but statistical reliability is low for these.