Today's diagnostics of hydronephrosis involve the necessary distinction between obstructive and nonobstructive dilatation of the urinary tract. Vagueness either in terminology or in the basic nature cannot be tolerated. Definition problems of partial obstruction of urotract result from the deficiencies of the methods applied when analyzing obstructions. Although the definition of the partial of urinary tract is not sufficiently comprehensive, it is nevertheless possible. Differencies in reliability of the most frequently used methods in the diagnostics of urotract obstruction result from the quality of information presented by the method. By appreciating the limits of the current diagnostical methods, failure in the interpretation of results obtained by their application may be avoided. A diuretic renogram, pressure flow test, usage of Doppler sonography with real-time sonography and well incorporated classical urography are methods of evaluation which make the diagnostics of urotract obstruction reliable and the treatment efficient.