Ryanair said its passenger numbers in September rose by 6% to 12.6 million despite two days of pilot and cabin crew strikes in five countries.
The airline had flown 11.8 million passengers the same time last year.
It said its load factor - how many seats it fills on each flight - was steady at 97%.
When passenger numbers from Laudamotion are included, total passenger numbers on Ryanair rose by 11% to 13.1 million last month, Ryanair added.
Ryanair had to cancel over 400 flights last month because of two days of strikes in five countries and repeated air traffic control staff shortages in the UK, Germany and France.
Shares in the airline had slumped yesterday after it cut its forecast for full-year profit by 12% and said worse may be to come if recent coordinated strikes across Europe continue to hit traffic and bookings.
Europe's largest low-cost carrier has struggled with labour relations since it decided to recognise trade unions for the first time last December.
Industrial unrest has escalated in recent months as it makes slow progress in talks with some unions.
Ryanair shares fell by as much as 13% on a warning that also cited higher oil costs and reverberated around the sector, with rivals Easyjet, Air France KLM and Lufthansa falling by 1.5-3%.
This 13% drop cut the airline's market capitalisation to just over €13 billion.
Meanwhile, Ryanair today announced a new route from Dublin to Bordeaux in France, with a twice-weekly service starting in April 2019.
The new route will be a part of Ryanair's Summer 2019 schedule.
Shares in the airline were lower again in Dublin trade today.