Aims/hypothesis This 52-week multinational, randomised, open-label, parallel-group, non-inferiority trial compared clinical outcomes following supplementation of oral glucose-lowering drugs with basal insulin analogues detemir and glargine in type 2 diabetic patients. Methods Insulin-naive adults (n = 582, HbA1c 7.5–10.0%, BMI ≤ 40.0 kg/m2) were randomised 1:1 to receive insulin detemir or glargine once daily (evening) actively titrated to target fasting plasma glucose (FPG) ≤ 6.0 mmol/l. An additional morning insulin detemir dose was permitted if pre-dinner plasma glucose (PG) was >7.0 mmol/l after achieving FPG < 7.0 mmol/l. Due to labelling restrictions, no second glargine dose was allowed. Results Baseline HbA1c decreased from 8.6 to 7.2 and 7.1% (NS) with detemir and glargine, respectively. FPG improved from 10.8 to 7.1 and 7.0 mmol/l (NS), respectively. With detemir, 45% of participants completed the study on once daily dosing and 55% on twice daily dosing, with no difference in HbA1c. Overall, 52% of participants achieved HbA1c ≤ 7.0%: 33% (detemir) and 35% (glargine) without hypoglycaemia. Within-participant variability for self-monitored FPG and pre-dinner PG did not differ by insulin treatment, nor did the relative risk of overall or nocturnal hypoglycaemia. Modest reductions in weight gain were seen with detemir vs glargine in completers (3.0 vs 3.9 kg, p = 0.01) and in the intention-to-treat population (2.7 vs 3.5 kg, p = 0.03), primarily related to completers on once-daily detemir. Mean daily detemir dose was higher (0.78 U/kg [0.52 with once daily dosing, 1.00 U/kg with twice daily dosing]) than glargine (0.44 IU/kg). Injection site reactions were more frequent with detemir (4.5 vs 1.4%). Conclusions/interpretation Supplementation of oral agents with detemir or glargine achieves clinically important improvements in glycaemic control with low risk of hypoglycaemia. Non-inferiority was demonstrated for detemir using higher insulin doses (mainly patients on twice daily dosing); weight gain was somewhat reduced with once daily insulin detemir. ClinicalTrials.gov ID no.: NCT00283751. Electronic supplementary material The online version of this article (doi:10.1007/s00125-007-0911-x) contains supplementary material, which is available to authorised users.