Abstract Context Estrogens underlie puberty in girls, but the steroid metabolome may also regulate pubertal timing in response to elevated stress and increasing body mass index (BMI). Objective Our objective was to identify steroid metabolome patterns linked to accelerated puberty and test whether BMI and stress markers modify this relationship. Methods From the LEGACY Girls Study, a longitudinal cohort followed for 6 years, we selected 327 girls aged 5 to 13 years at baseline to measure 36 steroid metabolites of glucocorticoids, androgens, progesterone, and estrogens in 2 urine samples collected before and during puberty. Parents reported the age at onset of breast development (thelarche), which had a high correlation in the subset with clinically assessed Tanner. Study staff measured height and weight and administered questionnaires, including the Internalizing Composite Scale, a parental proxy of child stress. We estimated hazard ratios (HRs) for the association between doubled steroid metabolites and ages at thelarche, pubarche, and menarche using Weibull survival models, testing interactions with stress and BMI z-scores. Results Accelerated thelarche was associated with higher prepubertal urinary metabolites of glucocorticoids (HR = 1.9, 95% CI: 1.5-2.5), androgens (HR = 3.9, 95% CI: 2.7-5.6), and progesterone (HR = 6.7, 95% CI: 4.1-10.9). Girls with high glucocorticoid metabolites combined with high BMI and stress reached thelarche 7 months earlier than their counterparts with low measures in these parameters. Conclusion Elevated metabolites of glucocorticoids, androgens, and progesterone are associated with accelerated pubertal onset, and BMI and stress modify this association. Previous studies have focused on estrogens, menarche, and BMI; our results suggest that androgens and stress impact the timing of thelarche as well, explaining secular declines in pubertal timing.