A climatology of polar-low evolution for seven low-sun seasons (November to March) in the North Pacific is presented. The data were collected by the subjective interpretation of Defense Meteorological Satellite Program (DMSP) infra-red imagery, using a cloud vortex classification scheme designed especially for use with medium to high resolution imagery. For the study period, about two-thirds of all polar lows that formed over the North Pacific evolved to a higher stage. Approximately one-half of those (one-third of the total) passed through all stages of development from cyclogenesis to decay. The more common form of cyclogenetic polar low in the North Pacific, the comma cloud, continued to develop two-thirds of the time, while the less common spiraliform only evolved to a higher stage of development in two-fifths of the cases. Those polar lows that formed in certain key areas were likely to evolve to a higher stage, while other specific locations discouraged continued development. No readily discernible difference between gross size and cloud characteristics of evolving and non-evolving polar lows was present in the satellite data, suggesting that additional data are needed to forecast correctly which will develop into mature cyclones.