Aspects of surficial, lateral, and apical sedimentation and erosion were evaluated in a two-year study of a coastal marsh. Net surficial deposition varied by habitat, season, and year. The marsh as a whole gained an estimated 0.65 cm of sediment the first year and 0.20 cm the next. Maximum deposition occurred in low-marsh habitats. Seasonal deposition increased from a minimum in autumn to a maximum in summer. Seasonal erosion was affected primarily by storm frequency; intensity of rainfall had little apparent influence. Map analyses, in the context of a salt marsh model, suggest that (1) marsh perimeters and total volumes of water accommodated by drainage systems in this area have not changed appreciably in more than 200 years, (2) lateral erosion at one site is offset by deposition at another; the principal net effect is channel meandering and stream piracy, (3) apical deposition and erosion are minimal, hence (4) the marsh, in spite of a submature stage of development, is nearly in equilibrium with the present coastal regime. Basic tenets of this model probably have application among numerous other southern marshes.