Background Ureteral atresia is the congenital absence of a ureteral opening, resulting in a blind-ended ureter that fails to terminate at the urinary bladder. Consequently, severe hydroureter and hydronephrosis occur ipsilateral to the atresic ureter. However, hydronephrosis contralateral to severe hydroureter, although reported in humans, is not documented in the dog. Additionally, ureteral atresia has not been reported as a cause for lower urinary tract signs directly related to extramural urinary bladder compression. This report aims to describe these unique manifestations of this congenital urinary tract disease, as well as follow-up findings after successful treatment. Case presentation A 4-month-old male Husky puppy was evaluated for pollakiuria, stranguria, and urine dribbling of 1-month duration. During the physical examination, a mass was palpated in the mid-abdomen. Diagnostic imaging and cystoscopy findings were diagnostic for right-sided ureteral atresia with secondary hydroureter and hydronephrosis. The severe right hydroureter caused lower urinary tract signs and contralateral hydronephrosis secondary to regional compression of the left distal ureter and urinary bladder. A right-sided ureteronephrectomy was performed, resolving the stranguria and pollakiuria. Significant reduction in the contralateral (left) hydronephrosis also occurred. Clinical Relevance Ureteral atresia should be considered as a differential diagnosis for lower urinary tract signs and/or bilateral hydronephrosis in a young dog. Reporting this case expands our knowledge of congenital lower urinary tract disease and the etiology of their manifestations in dogs. Surgical resolution of the congenital ureteral abnormality can result in preservation of renal function in the contralaterally obstructed kidney.Published version