The Sandanska Bistritsa takes its source from the south-eastern corner of the Tevnoto Lake in Northern Pirin at an altitude of 2,512 m. It flows in southern direction through another four lakes of the Malokamenishki Lakes group and then turns westwards. After the confluence with the first significant right tributary, the Bashliytsa, the turns to the south-west and flows in a deep sparsely forested valley. In the upper course of the river is located the Popinolashki waterfall, one of Pirin's largest. Near the town of Sandanski the river enters the Sandanski-Petrich Valley forming a large mucous cone. It flows into the Struma at an altitude of 104 m near the Sandanski industrial zone.