Temporal relationship between HS and obesity is not established. To compare baseline BMI and change in BMI between HS patients and controls before and after diagnosis. Retrospective case-control analysis of 1,284 HS patients and controls matched on age, sex, race, and calendar year between January 1, 1999 and September 9, 2019. BMI 7 years prior to first HS diagnosis, and rate of BMI change, were compared between HS patients and controls using linear mixed effects models. Baseline BMI was higher among HS patients than controls [mean difference = 3.03 kg/m2 (95% CI 2.44-3.62; p<0.001)]. This difference was larger for women [mean difference = 3.37 kg/m2 (95% CI 2.73, 4.01)] than men [mean difference =1.27 kg/m2 (95% CI -0.20, 2.73; interaction p=0.01)], as well as for HS patients diagnosed before age 40 years [mean difference = 4.10 kg/m2 (95% CI, 3.15, 5.06)] than those diagnosed after age 40 years [mean difference = 2.38 kg/m2 (95% CI, 1.63, 3.12; interaction p<0.001)]. Prior to diagnosis, average annual increase in BMI among HS patients was slightly higher than controls. There was no statistically significant change in annual BMI among HS patients following diagnosis. Baseline BMI and, to a lesser extent, rate of BMI change appear to be risk factors for developing HS. Influence of BMI may play a larger role among female and younger patients.