A dishwashing machine having a load-bearing structure (2, 5) and a washtub, there being articulated to the load-bearing structure (2, 5) a front door of the tub, the machine moreover having a system for extraction of damp air from the tub, which comprises a fan and a discharge duct having a hollow body with a width dimension of and a height dimension, wherein the fan is a radial fan having a fan housing housed in which is a centrifugal impeller, the fan housing having an intake mouth and a delivery, wherein the discharge duct has an inlet portion and an outlet portion, the intake mouth of the fan housing being in fluid communication with an outlet opening of the tub, the inlet portion of the discharge duct being in fluid communication with the delivery of the fan housing, and the outlet portion of the discharge duct being at the front of the machine, wherein at least the outlet portion and the intermediate portion of the discharge duct extend above an upper wall of the tub, with the outlet portion above an upper edge of the door, wherein the outlet opening is formed in one of the upper wall and a stationary side wall of the tub, with the fan housing, which is mounted on said wall (3a; 3c) with the respective intake mouth at the outlet opening and set substantially coaxial thereto, in such a way that damp air is drawn in from the outlet opening substantially in the direction of the axis of the impeller and forced in a radial direction into the discharge duct, and then expelled from the outlet portion at the front of the machine above the upper edge of the door; the dishwashing machine being characterized in that: - the discharge duct has a portion intermediate with respect to the inlet and outlet portions (10, 11), the height of which decreases in a substantially progressive way towards the outlet portion and the width of which increases in a substantially progressive way towards the outlet portion and - at least one of an upper wall and a lower wall of the intermediate portion of the discharge duct is generally plane and set horizontally, whereas the other of the upper wall and the lower wall of the intermediate portion is generally inclined starting from the inlet portion of the discharge duct towards its outlet portion. wherein the fan is a radial fan having a fan housing housed in which is a centrifugal impeller, the fan housing having an intake mouth and a delivery, wherein the discharge duct has an inlet portion and an outlet portion, the intake mouth of the fan housing being in fluid communication with an outlet opening of the tub, the inlet portion of the discharge duct being in fluid communication with the delivery of the fan housing, and the outlet portion of the discharge duct being at the front of the machine, wherein at least the outlet portion and the intermediate portion of the discharge duct extend above an upper wall of the tub, with the outlet portion above an upper edge of the door, wherein the outlet opening is formed in one of the upper wall and a stationary side wall of the tub, with the fan housing, which is mounted on said wall (3a; 3c) with the respective intake mouth at the outlet opening and set substantially coaxial thereto, in such a way that damp air is drawn in from the outlet opening substantially in the direction of the axis of the impeller and forced in a radial direction into the discharge duct, and then expelled from the outlet portion at the front of the machine above the upper edge of the door; the dishwashing machine being characterized in that: - the discharge duct has a portion intermediate with respect to the inlet and outlet portions (10, 11), the height of which decreases in a substantially progressive way towards the outlet portion and the width of which increases in a substantially progressive way towards the outlet portion and - at least one of an upper wall and a lower wall of the intermediate portion of the discharge duct is generally plane and set horizontally, whereas the other of the upper wall and the lower wall of the intermediate portion is generally inclined starting from the inlet portion of the discharge duct towards its outlet portion. - the discharge duct has a portion intermediate with respect to the inlet and outlet portions (10, 11), the height of which decreases in a substantially progressive way towards the outlet portion and the width of which increases in a substantially progressive way towards the outlet portion and - at least one of an upper wall and a lower wall of the intermediate portion of the discharge duct is generally plane and set horizontally, whereas the other of the upper wall and the lower wall of the intermediate portion is generally inclined starting from the inlet portion of the discharge duct towards its outlet portion.