A pressure monitoring apparatus (1) for monitoring pressure of a liquid (4) in a vessel (2) comprises a housing (3) within which an airtight gas chamber (6) is formed. A pressure sensor (8) is located in the housing (3) monitors the pressure of a gas in the gas chamber (6). A conduit (12) having a communicating bore (16) of total length Lt communicates the gas chamber (6) with the vessel (2). As the pressure of the liquid in the vessel (2) increases, a liquid/gas interface meniscus (20) travels along a working length Lw of the communicating bore (16) from the second end (15) thus increasing the pressure in the gas chamber (6) to the pressure of the liquid, which is monitored by the pressure sensor (8). The total length Lt of the conduit (12) is greater than the working length Lw of the conduit (12) to avoid the liquid/gas interface meniscus (20) reaching the first end (14) of the communicating bore (16). The pressure monitoring apparatus (1) may also be mounted at the distal end (33) of a balloon catheter (30) for monitoring the pressure of a liquid inflating medium inflating the balloon (35) of the balloon catheter (30), which may be an electrically conductive liquid, with the gas isolating the pressure sensor (8) from the liquid inflating medium.