The invention relates to a sensor and guide wire assembly (21 41 61 81) for intravascular measurements of a physiological variable in a living body, comprising a sensor element (22 42 62 82) mounted at a distal sensor portion (23 43 63 83) of a guide wire (24 44 64 84), wherein said sensor portion exhibits a maximal cross-sectional dimension which is larger than a maximal cross-sectional dimension of guide wire portions (28, 30 48, 50 68, 70) located proximally of said sensor portion.