To assess the influence of health locus of control and fear of hypoglycaemia on metabolic control and treatment satisfaction in people with Type 1 diabetes mellitus on continuous subcutaneous insulin infusion. People with Type 1 diabetes on continuous subcutaneous insulin infusion for at least 1 year, sub-classified as an 'acceptable glucose control' group [HbA1c ≤ 58 mmol/mol (7.5%)] and a 'suboptimum glucose control' group [HbA1c > 58 mmol/mol (7.5%)], were consecutively enrolled in a multicentre cross-sectional study. Questionnaires were administered to assess health locus of control [Multidimensional Health Locus of Control (MHLC) scale, with internal and external subscales], fear of hypoglycaemia [Hypoglycaemia Fear Survey II (HFS-II)] and treatment satisfaction [Diabetes Treatment Satisfaction Questionnaire (DTSQ)]. We enrolled 214 participants (mean ± sd age 43.4 ± 12.1 years). The suboptimum glucose control group (n = 127) had lower mean ± sd internal MHLC and DTSQ scores than the acceptable glucose control group (19.6 ± 5.2 vs 21.0 ± 5.0, P = 0.04 and 28.8 ± 4.8 vs 30.9 ± 4.5, P < 0.001). HFS-II scores did not differ between the two groups. Internal MHLC score was negatively associated with HbA1c (r = -0.15, P < 0.05) and positively associated with the number of mild and severe hypoglycaemic episodes (r = 0.16, P < 0.05 and r = 0.18, P < 0.001, respectively) and with DTSQ score (r = 0.17, P < 0.05). HFS-II score was negatively associated with DTSQ score (r = -0.18, P < 0.05) and positively with number of severe hypoglycaemic episodes (r = 0.16, P < 0.5). In adults with Type 1 diabetes receiving continuous subcutaneous insulin infusion, high internal locus represents the most important locus of control pattern for achieving good metabolic control.