The town is located on the Via Emilia, a major thoroughfare for town traffic, 6 kilometres (4 mi) from the city centre of Bologna towards the southeast.

The territory of the municipality extends towards the plain and at the foot of the first hills around Bologna. Some watercourses such as the Zena (creek), the Idice and the Savena, after which the town was named, flow through the town.

Within the territory of the municipality we can find the Spipola Cave with its doline and the chalky rock emergences of the Farneto and the Croara, that give shape to a karst compound (there are about 50 caves and natural hollows crossed by a 6-kilometre (4 mi) long hypogeous stream), protected by the Parco dei Gessi Bolognesi e Calanchi dell'Abbadessa (Natural park of Bologna's chalky rocks and the Abbess's gully).

The area of San Lazzar has been inhabited since ancient times, as testified by findings from the Stone Age (stone implements) and the Bronze Age; along with nearby Castenaso, it witnessed a flourishing Villanovian civilization.

Documents state the site for the town once housed a lazzaretto or leprosarium. These were often located outside of cities where people could be segregated from the population.

The town was autonomous municipality in the Napoleonic Era (1810). It was afterwards readmitted to Bologna and gained back autonomy with the help of Carlo Berti Pichat after 1827.

Nowadays, after the building expansion of the 1970s, San Lazzaro is one of the most populated towns in the province of Bologna and is the main seat of a large number of factories.

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Wikipedia