BACKGROUND: Overweight/obesity (OW) is linked to worse asthma and poorer inhaled corticosteroid (ICS) response in older children and adults. OBJECTIVE: We sought to describe the relationships between OW and asthma severity and response to ICS in preschool children. METHODS: This post hoc study of 3 large multicenter trials involving 2- to 5-year-old children compared annualized asthma symptom days and exacerbations among normal weight (NW) (body mass index: 10th-84th percentiles) versus OW (body mass index: >/=85th percentile) participants. Participants had been randomized to daily ICS, intermittent ICS, or daily placebo. Simple and multivariable linear regression was used to compare body mass index groups. RESULTS: Within the group not treated with a daily controller, OW children had more asthma symptom days (90.7 vs 53.2, P = .020) and exacerbations (1.4 vs 0.8, P = .009) thanNW children did. Within the ICS-treated groups, OW and NW children had similar asthma symptom days (daily ICS: 47.2 vs 44.0 days, P = .44; short-term ICS: 61.8 vs 52.9 days, P = .46; as-needed ICS: 53.3 vs 47.3 days, P = .53), and similar exacerbations (daily ICS: 0.6 vs 0.8, P = .10; short-term ICS: 1.1 vs 0.8 days, P = .25; as-needed ICS: 1.0 vs 1.1, P = .72). Compared with placebo, daily ICS in OW led to fewer annualized asthma symptom days (90.7 vs 41.2, P = .004) and exacerbations (1.4 vs 0.6, P = .006), while similar protective ICS effects were less apparent among NW. CONCLUSIONS: In preschool children off controller therapy, OW is associated with greater asthma impairment and exacerbations. However, unlike older asthmatic patients, OW preschool children do not demonstrate reduced responsiveness to ICS therapy.