INS and diabetes mellitus: The group of adolescents with poor glycaemic control was characterised by significantly longer diabetes duration (6.7 ± 4.3 vs. 3.9 ± 3.1 years, p = 0.005), higher insulin dose (0.86 ± 0.22 vs. 0.67 ± 0.16 U/kg bw/d, p = 0.005) which is strictly connected with HbA1c levels, older age (16.0 ± 1.7 vs. 14.4 ± 1.8 years, p = 0.001), and lower body height values (SD score) (i.e., −0.34 ± 1.02 vs. +0.38 ± 1.10, p = 0.012), compared to patients with good glycaemic control.