Overpressure zones in sedimentary basins are defined as sediments where the fluid pore pressure is substantially higher than hydrostatic. Chief among the causes for the formation of overpressure is the rapid deposition of low-permeability sediments so that compaction and dewatering are inhibited. This results in the support of the overlying material in part by the fluid, rather than by grain to grain contact. Many overpressure zones also have associated geothermal anomalies whereby the geotherms are hotter than normal. In this paper, we present a one-dimensional model of overpressure generation and dissipation, with hydraulic fracture. The fluid flow is coupled to the fluid temperature field and to the motion of the solid sediment matrix. Compacted coordinates are introduced to decouple the fluid velocity and temperature from the solid matrix velocity. Using a maximum sedimentation rate of 1 km Myr-1 and a hydraulic conductivity at the top of the layer equal to 5¿10-12 m s-1, 3 km of partially compacted sediment are deposited in 5 Myr, generating an overpressure of 0.81 of the lithostatic pressure at the bottom of the sediment layer. An undercompaction of 19% relative to normally compacted sediment is developed at a final depth of 3.66 km by the end of sedimentation. Dissipation of the overpressure takes place on a timescale of the order of 40 Myr. The equilibrium temperature generates thermal gradients in excess of 38 ¿C km-1 at shallow depths. Fast sedimentation rate and high permeability in the fractured state favor oscillating behavior and propagation of fracture waves. Overpressure zones may constitute a proximal source of hydrothermal fluids for the genesis of ore deposits in sedimentary basins. ¿ 2000 American Geophysical Union