The Lambro rises from the Monte San Primo (1,685 m) near the Ghisallo, in the province of Como, not far from Lake Como. After Magreglio it flows through the Vallassina and the comuni of Asso, Ponte Lambro and Erba, entering Lake Pusiano with the name of Lambrone. Later it passes through Brianza reaching Monza and crossing its famous park (where king Umberto I was assassinated by Gaetano Bresci) in two branches which join again before the river passes through the eastern part of Milan. At Melegnano it receives the waters of the Vettabbia and, at Sant'Angelo Lodigiano, those of its main tributary, the Lambro meridionale (or “Southern Lambro”), almost doubling its discharge. The Lambro flows into the Po near Orio Litta.
At 5.8 m³/s the average discharge of the Lambro is relatively small, but it can be occasionally boosted to 40 m³/s or more by the Milanese water drains and dangerous floods are frequent in the rainy seasons. Also a name of Innocenti's popular three wheeler commercial transport vehicle