Church of San Gregorio, Baroque church in Monza, Italy

San Gregorio is a hexagonal oratory begun in 1680, its dome added in 1748 after models by Bernardo Antonio Vittone, mixing Baroque and Rococo elements. The pale stucco facade has a portico of round arches on square pilasters, a triangular pediment above, and a small square bell tower with a pyramidal cap behind. A U-shaped portico section survives as its pronaos.

Construction of the hexagonal oratory began in 1680 on the site of a plague cemetery known as the "foppone", funded by Carlo Francesco dei conti Durini, feudal lords of Monza since 1650. The design is attributed to pupils of Richino, and the dome was added in 1748 following models by Bernardo Antonio Vittone. The building was later enclosed by U-shaped porticoes of the San Gregorio cemetery, which closed in 1930.

Since 2003 the oratory has been granted for use to the Romanian Orthodox parish "Tutti i Santi" of the Romanian Orthodox Patriarchate, whose priest is Father Pompiliu Nacu. Mass is celebrated every Wednesday, Friday and Sunday, each time attended by more than 1000 believers from the Romanian community of Monza and Brianza.

The oratory stands outside Monza's historic centre, southeast of it in a bend of the Lambro, near the 1840 railway station and the old Davide Guarenti stadium. The former cemetery road from via Milano was closed for safety as rail traffic grew, so the approach now comes from via Aliprandi and the piazza Castello level crossing. The Romanian Orthodox parish celebrates Mass on Wednesdays, Fridays and Sundays.

Since 2003 the oratory has been granted to the Romanian Orthodox parish "Tutti i Santi" of the Romanian Orthodox Patriarchate, whose priest is Father Pompiliu Nacu. Mass is held every Wednesday, Friday and Sunday, each time attended by more than 1,000 believers from Monza and Brianza.