Background: Intergenerational social mobility is hypothesized to be a stressful process that has a negative effect on health. By examining the relationship between own socioeconomic position, parental socioeconomic position, and allostatic load in a representative sample of the British population, we test this hypothesis. Methods: Our study uses cross-sectional data from 9,851 adult participants of waves 2 and 3 of Understanding Society. The relationship between parental occupational class at age 14, respondents’ social class at the time of the interview, and allostatic load (AL) is explored by means of diagonal reference models (DRM), which allow us to disentangle the effects of parental social class, own social class, and the mobility process. The AL score comprises the biomarkers 1) total cholesterol, 2) HDL cholesterol, 3) triglycerides, 4) glycated haemoglobin, 5) C-reactive protein, 6) fibrinogen, 7) systolic blood pressure, 8) diastolic blood pressure, 9) resting heart rate, 10) BMI, and 11) waist circumference. Results: AL is particularly high among the stable working class and low among the stable upper class. On average, current class and origin class exert about equal weight on current AL. However, social mobility—regardless of whether upwards or downwards—is not detrimental for AL. Further, we find evidence that class of origin may be less important among those outside the labor market for reasons other than retirement. Conclusion: Both own social class and parental social class influence AL to a similar extent. However, we find no evidence that mobility trajectories exert any effects, good or bad, on allostatic load.