['High serum angiotensin-converting enzyme (ACE) activity is associated with increased risk of severe hypoglycaemia (SH) within 1 year in type 1 diabetes. We wanted to find out whether ACE activity is stable over time and predicts SH beyond 1 year, and if gender differences exist in the association between ACE activity and risk of SH.', 'A follow-up study of 128 adult patients with type 1 diabetes was conducted. At entry, ACE activity was measured. For 12 months, patients prospectively recorded events of severe hypoglycaemia (SH). At a median of 40 months, ACE activity was measured again and participants recalled the number of SH in the last year.', 'ACE activity is reproducible over 40 months (p < 0.00001). Patients with SH during the baseline study also had SH during follow-up (p < 0.00001). Serum ACE activity measured at baseline was positively associated with the rate of SH at follow-up (p = 0.0003) with a 3.2-fold increased rate of SH in subjects belonging to the upper ACE quartile compared to subjects in the three lowest quartiles (p < 0.00001). The association between high serum ACE activity and increased risk of SH did not differ significantly in women and men.'] Does high serum ACE activity predict severe hypoglycaemia over time in patients with type 1 diabetes?