CONTEXT: Few studies have assessed factors associated with severe hypoglycemia (SH) and diabetic ketoacidosis (DKA) in adults with type 1 diabetes (T1D). OBJECTIVE: Our objective was to determine frequency of and factors associated with the occurrence of SH and DKA in adults with T1D. DESIGN AND SETTING: We conducted a cross-sectional analysis from the T1D Exchange clinic registry at 70 U.S. endocrinology centers. PATIENTS: Analysis included 7012 participants in the T1D Exchange clinic registry aged 26 to 93 years old with T1D for >/=2 years. RESULTS: Higher frequencies of SH and DKA were associated with lower socioeconomic status (P < .001). SH was strongly associated with diabetes duration (P < .001), with 18.6% of those with diabetes >/=40 years having an event in the past 12 months. SH frequency was lowest in those with hemoglobin A1c (HbA1c) levels of 7.0% (53 mmol/mol) to 7.5% (58 mmol/mol), being higher in those with HbA1c levels <7.0% (<53 mmol/mol) or >7.5% (>58 mmol/mol). DKA frequency increased with higher HbA1c levels (P < .001), with 21.0% of those with HbA1c >/=10.0% (>/=86 mmol/mol) having an event in the past 12 months. CONCLUSIONS: SH and DKA are more common in those with lower socioeconomic status. DKA, most common in those with HbA1c >/=10.0% (>/=86 mmol/mol), should be largely preventable. In contrast, SH, most frequent with diabetes >/=40 years duration, cannot be abolished given the limitation of current therapies. To reduce SH in adults with longstanding diabetes, consideration should be given to modifying HbA1c goals, particularly in patients with very low HbA1c levels.