We determined the association between gestational weight gain and severe maternal morbidity. We used data on 84,241 delivery hospitalizations at Magee-Womens Hospital, Pittsburgh, PA (2003–2012). Total gestational weight gain (kilogram) was converted to gestational age–standardized z-scores. We defined severe maternal morbidity as having ≥1 of the 21 Centers for Disease Control diagnosis or procedure codes for severe maternal morbidity identification, intensive care unit admission, or extended postpartum stay. We used multivariable logistic regression to determine the association between weight gain and severe maternal morbidity after confounder adjustment. High gestational weight gain z-scores were associated with an increased risk of severe maternal morbidity. Compared with z-score 0 SD (equivalent to 16 kg at 40 weeks in a normal-weight woman), risk differences (95% confidence intervals) for z-scores −2 SD (7 kg), −1 SD (11 kg), +1 SD (23 kg), and +2 SD (31 kg) were 1.5 (−0.71, 3.7), 0.056 (−0.81, 0.93), 3.4 (1.7, 5.0), and 8.6 (4.0, 13) per 1000 deliveries. The results did not vary by gestational age at delivery or prepregnancy body mass index. The increased risk of severe maternal morbidity with high pregnancy weight gain may allow scientists to understand and prevent this serious condition.