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

Return flights

23 Sep - 01 Oct	Delta
29 Sep - 07 Oct	Delta
28 Sep - 07 Oct	Delta
15 Sep - 22 Sep	Delta
15 Sep - 30 Sep	KLM
23 Sep - 29 Sep	Delta
21 Sep - 14 Oct	Delta
22 Sep - 29 Sep	Delta
15 Sep - 29 Sep	Delta
08 Sep - 15 Sep	Delta
09 Sep - 17 Sep	Delta
09 Sep - 16 Sep	Delta
12 Sep - 18 Sep	Delta
12 Sep - 16 Sep	Delta
08 Sep - 04 Oct	Frontier Airlines
30 Sep - 25 Oct	Virgin Atlantic
10 Sep - 04 Oct	KLM
23 Sep - 18 Oct	Air France
22 Sep - 18 Oct	Air France
26 Sep - 18 Oct	Air France

Also check the deals for one-way flights from Chicago 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 Chicago to Madrid in September from $437

Return flights