AirHint found the following cheapest return flights from Chicago (MDW) to Lisbon (LIS) in August 2025 (see full year).

Return flights

20 Aug - 30 Aug	Delta
20 Aug - 31 Aug	Delta
20 Aug - 28 Aug	Delta
30 Aug - 20 Sep	Frontier Airlines
21 Aug - 28 Aug	Frontier Airlines
30 Aug - 02 Sep	Frontier Airlines
21 Aug - 30 Aug	Frontier Airlines
28 Aug - 30 Aug	Frontier Airlines
24 Aug - 31 Aug	Frontier Airlines
22 Aug - 28 Aug	Frontier Airlines
29 Aug - 01 Sep	Frontier Airlines
20 Aug - 21 Aug	Frontier Airlines
23 Aug - 30 Aug	Delta

Also check the deals for one-way flights from Chicago to Lisbon in August.

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 Lisbon in August from 696€

Return flights