Abstract: A toilet seat assembly comprising a seat for permitting a user to sit over a toilet bowl of a toilet apparatus and a hinge pivotally attaching the seat to the toilet apparatus so that the user can manually pivot the seat relative to the toilet bowl between a vertical-upright position and a horizontal-down position. The hinge has a lock which automatically engages when the seat is manually pivoted into the vertical-upright position to prevent the seat from inadvertently pivoting back to the horizontal-down position. The toilet seat assembly can be further provided with a lid for selectively covering the toilet seat. The hinge lock can be adapted to automatically engage when the lid is manually pivoted into the vertical-upright position to prevent the lid from inadvertently pivoting back to the horizontal-down position.