A light variability study in NGC 2264 shows that about 25 % of the pre-main sequence A and F stars show irregular short-period variability and/or brightness changes since 1953. There exists a good correlation between this variability and (other) shell indicators. The scatter in the pre-main sequence band in the color-magnitude diagram can be partially explained by shells and an age spread between 1 and 3 × 106 years is indicated. W 90, a star below the main sequence, has brightened by half a magnitude to V = 12.5 since 1953. The corresponding color variation suggests a ratio of total to selective extinction of about 9.