The present study aimed to assess the impact of diurnal mouthpiece intermittent positive pressure ventilation(MIPPV) as the extension of the nasal intermittent positive pressure ventilation (NIPPV) in Duchennemuscular dystrophy (DMD). In total, 42 DMD patients aged 15-33 yrs, normocapnic at night with NIPPV and receiving MIPPV since end-diurnal hypercapnia, were studied. Transcutaneous CO2 tension (Pt,CO2) was prospectively monitored at the end of the day, before and after MIPPV initiation. Vital capacity (VC), breathing pattern and maximal inspiratory strength were measured. Patients were asked to score the presence (1 point) or absence (0 point) of seven respiratory-linked symptoms before and after MIPPV establishment. Survival rates reached 88, 77, 58 and 51% after 1, 3, 5 and 7 yrs, respectively. The mean survival rate was 31 yrs. VC stabilised during 5 yrs with MIPPV. Symptom scores significantly decreased and Pt,CO2 normalised during the day (8.17 +/- 2.22 to 5.78 +/- 0.73 kPa). No accident and minor side-effects were observed in this 184 cumulated patient-yrs study. In conclusion, daytime mouthpiece ventilation is safe, prolongs survival and stabilises vital capacity in Duchenne muscular dystrophy patients. It is recommended on the condition that patients are equipped with a self-supporting harness.