The effects of temperature variations on the tilt measured by long fluid tube tiltmeters are examined in detail. Temperature effects are important both in instruments which measure tilt as changes in fluid pressure. Methods are outlined for reducing temperature effects in both types of tiltmeters. A New temperature-compensating method for fluid pressure tiltmeters is demonstrated both in theory and in practice. The method requires that the fluid-filled tube(s) connecting the pressure transducer to the end reservoir(s) be laid at a constant small angle to to the horizontal. Tiltmeter which use a horizontal half-filled fluid tube are recommended on the grounds of long-term stability and freedom from temperature effects.