The intrinsic diameters of the nine Trumpler classes of open clusters are reexamined. For unreddened or slightly reddened clusters, photometric data are used to find distances and intrinsic diameters of three Trumpler classes. An examination of reddened clusters of these classes indicates no systematic variation in the ratio of total to selective absorption with galactic longitude. Photometric distances and Trumpler's angular diameters are then used to calculate mean intrinsic diameters of the nine Trumpler classes.