The 1990 O'Byrne Cup was a Gaelic football competition contested by the county teams of Leinster GAA.

The tournament format was straight knockout, with 11 participating teams. Dublin did not enter the competition. First-round byes were awarded to Laois, Louth, Meath, Longford and Kildare.

Louth won the competition after defeating Kildare in the final, held at the Drogheda Gaelic Grounds.

	First round 7 - 14 April					Quarter-finals 14 - 18 April					Semi-finals 21 - 25 April					Final 23 May
	Wexford		3-09
	Wicklow		0-04			Wexford		0-12
						Laois		2-05
											Wexford		1-04
	Carlow		2-13								Kildare		2-11
	Kilkenny		1-06			Carlow		1-09
						Kildare		1-12
																Kildare		1-06
	Westmeath		0-11													Louth		2-04
	Offaly		0-11			Louth		1-12
						Meath		2-06
											Louth		2-11
	Westmeath		1-08								Longford		1-13
	Offaly		1-07			Westmeath		1-09
						Longford		2-08

23 May 1990^[1][2]

Louth	2-04 - 1-06	Kildare

Gaelic Grounds

Referee: D. Guerin (Dublin)