Knowledge gaps exist for life-history attributes of common yet secretive species, such as many plethodontid salamanders, which are often difficult to observe. Study of museum specimens supplemented by chance field observations can help address these knowledge gaps. There is a paucity of information on the reproduction and life cycle of Plethodon dorsalis (Northern Zigzag Salamander). We examined 131 preserved specimens collected monthly from southern Illinois to better understand the female reproductive cycle. We also report observations of egg-brooding. We found females containing 2–7 ovarian follicles (mean = 5.03) in March, April, October, and November, and there was a relationship between SVL and number of developing ovarian follicles (P = 0.04). We observed and photographed 5 Northern Zigzag Salamanders brooding clutches of 4–6 eggs (mean = 5) on the walls within 3 small caves during June and July. More study is needed to better understand the natural history of this geographically widespread but overlooked species and its unusual behavior.