AbstractWe describe the physiological and behavioral maturity of the red deep-sea crab, Chaceon quinquedens (Smith, 1879), using ovary and oocyte development and morphological features to estimate the size at 50% sexual maturity (SM50) for females in the Mid-Atlantic Bight. This economically important species inhabits the continental shelf and slope of the western Atlantic from Nova Scotia, Canada to the Gulf of Mexico. Samples were collected by trawling in 2011–2013 and by traps in 2014–2016. We used histological analysis to describe the stages of ovarian development. Five stages of ovarian development were identified: 1, immature; 2, early maturing; 3, late maturing; 4, mature; and 5, redeveloping. A logistic model was used to estimate the SM50 using maximum likelihood methods. Physiological SM50 varied among geographic locations and was estimated at 61.2 mm CL and 70.8 mm CL for females collected near Hudson Canyon and Baltimore and Norfolk canyons, respectively. Behavioral SM50 decreased with latitude and was estimated at 53.9 mm CL, 62.5 mm CL and 65.5 mm CL for Hudson, Baltimore, and Norfolk canyons, respectively. Results implied asynchrony between physiological and behavioral sexual maturity, suggesting that mating occurs prior to completion of ovarian development. This study provides the first evidence of a latitudinal trend in sexual maturity for C. quinquedens. Further investigation is needed to understand the cause of the latitudinal trend as our study presented limitations. Results provide useful information for fisheries management about the reproductive biology of C. quinquedens.