AirHint found the following cheapest return flights from St. Louis (STL) to Madrid (MAD) in September 2025 (see full year).

Return flights

23 Sep - 07 Oct	Air Canada
24 Sep - 01 Oct	Iberia
30 Sep - 07 Oct	Iberia
21 Sep - 28 Sep	Iberia
09 Sep - 16 Sep	United
02 Sep - 09 Sep	Iberia
27 Sep - 04 Oct	Iberia
15 Sep - 22 Sep	United
18 Sep - 25 Sep	Iberia
04 Sep - 11 Sep	Air Canada
12 Sep - 19 Sep	Iberia
06 Sep - 13 Sep	United

Also check the deals for one-way flights from St. Louis to Madrid in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from St. Louis to Madrid in September from $564

Return flights