We examined reproduction over 3 yr using radio telemetry and X-rays in a South Carolina population of spotted turtles (Clemmys guttata). Spring courtship (March–April) coincided with aggregations of turtles; however, a second peak in courtship in the fall (September–October) did not coincide with such aggregations. Over 75% of the radio-tagged females were gravid in each year of the study. The nesting season lasted approximately two months (mid-May through mid-July). Nesting was primarily nocturnal, and most nests (17/21, 81%) were made in the woody debris of decaying logs and stumps. Incubation time (mean = 79 d) decreased as nest temperature increased. Clutch size was not correlated to maternal body size, and we found no evidence for a tradeoff between clutch size and egg size. However, all measures of egg size and most measures of hatchling size were independent of maternal body size. We also compared reproduction among three widely separated populations of spotted turtles. Clutch size varied with latitude: clutch size was largest in the north (Ontario, mean = 5.3 eggs), mid-sized in the central population (Pennsylvania, mean = 3.9), and smallest in the south (South Carolina, mean = 2.8). Variation in reproductive output among populations was attributable to both variation in number of eggs and to egg size. Most of this variation in clutch size and egg size was explained by differences in body size of females among populations. Because the spotted turtle is considered to be a Species at Risk throughout its range, the data provided in the current study will be useful in conservation planning and for directing future research on the reproductive ecology of freshwater turtles.