Background: Ventilator induced diaphragmatic dysfunction (VIDD), as a loss of diaphragmatic force generating capacity due to the use of mechanical ventilation. Difficulties in discontinuing ventilatory support are encountered in 20–25% of mechanically ventilated patients, with a staggering 40% of time spent in the intensive care unit being devoted to weaning. M-mode ultrasonography is now an accepted qualitative method of assessing diaphragmatic motion in normal and pathological conditions. In this study, we evaluated whether diaphragmatic excursion (DE) as measured by M-mode Sonography can be a predictor of weaning and diagnosis of VIDD. Methods: Fifty consecutive patients who required mechanical ventilation ≥72hrs. who fulfilled the spontaneous breath trial (SBT) criteria, at the start of a 1-hr SBT, each hemidiaphragm was evaluated M-mode Sonography with the patient in the supine position. Rapid shallow Breathing index (RSBI) was simultaneously calculated at the bedside. Ultrasonographic Diaphragmatic Dysfunction (DD) was diagnosed if an Diaphragmatic Excursion (DE) was <10 mm or negative, the latter indicating paradoxical diaphragmatic movement.Results: Diaphragmatic Dysfunction DD among the eligible 50 patients was 48% (n = 24). DD group had longer weaning time [43 (192–10) hrs. vs. 29 (72–11) hrs. p = 0.02) in DD vs. NDD group respectively and total ventilation time [144 (480–72) hrs. vs. 139 (336–72) hrs. p > 0.05) in DD vs. NDD group respectively. Weaning failure was (45.8% vs. 30.8%, p=0.01) in DD vs. NDD group respectively. In NDD group Rt. DE, mean 24.7 ±8.7mm, IQR 17.25 mm and median 23.4mm (40-11.5). While Lt. side was 23.2±7.7mm, 11.25mm and 22mm (45-15) respectively. In DD group Rt. DE, mean 7.6 ±2.02mm, IQR 2.4 mm and median 8.2mm (10-1.9). While Lt. side was 9.2±0.8mm, 4.3mm and 8.9mm (9.8-5.7) respectively. The area under ROC of ultrasonographic criteria in predicting weaning failure was near similar to that of rapid shallow breathing index. Conclusions: DD is present in a significant percentage 48% nearly half of our medical ICU patients on MV ≥72hrs.DE as a morphometric index is as good as traditional volumetric respiratory indices in predicting weaning outcome.PaCO2 was higher in NDD, suggesting the protective role of hypercapnia against DD.