A model for quantitative analysis of microdisk laser emission spectra is presented. Conformal mapping is used to determine radial and azimuthal eigenvalues, eigenvectors, and cavity Q corresponding to leaky optical resonances in an optically transparent dielectric disk. The effects of gain and loss in a microcavity active medium are also included in the model. Our results compare well with experimental data obtained from,an InGaAs/InGaAsP quantum well microdisk laser of radius R=0.8 mu m. (C) 1996 American Institute of Physics.802644653