Abstract: Introduction: Among the urinary bladder masses, urinary bladder cancer is the most commonly diagnosed malignancy in patients presenting with haematuria. Early detection is crucial for improving patient prognosis. The diagnostic modalities commonly used to evaluate patients with bladder mass include IVU, transabdominal ultrasonography (USG), computed tomography (CT) and cystoscopy. Of them transabdominal ultrasonography has been proposed as screening test for detection of bladder mass, but its accuracy is still a dispute. Objective: The present cross-sectional study is aimed to find the diagnostic accuracy of Trans abdominal USG in differentiating benign from malignant bladder masses. Methodology: This cross-sectional study was carried out in the Department of Radiology & Imaging, Dhaka Medical College Hospital, Dhaka between January 2014 to June 2014. 60 adult patients with diagnosis of bladder mass made by intravenous urography or clinically suspected or recurrence case were the study population and were consecutively included in the study. Trans-abdominal ultrasonography was performed in each patient and a ultrasound diagnosis was made. Histopathology was done and using formulae accuracy, sensitivity, specificity, positive and negative predictive values of the trans-abdominal USG in diagnosing bladder masses were done. Result: More than 70% of the patients were 55 years old or more with mean age of 58.3 years. A male preponderance was observed in the series. Painless hematuria was the predominant complaint (90%), followed by frequency of micturition (78.3%), urgency (70%), dysuria (63.3%), retention of urine 45% and low-back pain (31.7%). The study demonstrated a high sensitivity (94.5%) and moderate specificity (60%) of trans-abdominal ultrasound in the diagnosis of bladder mass. The overall diagnostic accuracy was appreciably high (91.7%). Conclusion: The study concluded that Transabdominal USG can differentiate bladder carcinoma from benign bladder mass with fair degree of accuracy showing results of high sensitivity, high accuracy and a moderate specificity.