By using the 6 step ladder protocol algorithm suggested by us one can attempt to distinguish the hydronephrotic variant of multicystic dysplastic kidney from the hydronephrotic kidney due to pelviureteral obstruction in patients presenting with a symptomatic cystic flank masses of renal origin. Differentiation between the two may be difficult at times due to the medial/central placement of cysts in the former. This is necessary since renal salvage may be possible in the latter while timely nephrectomy may be considered in the former to prevent against the hazards of leaving behind a dysplastic kidney in situ.