How many skill checks do you have to pass for a ritual to succed?

[Yqatuba]

Is it just one?

[breithauptclan]

Yes. Just the primary check has to succeed.

Casting Rituals wrote:

Checks: At the ritual’s culmination, you must attempt the skill check listed in the Primary Check entry to determine the ritual’s outcome.

Secondary Casters: Secondary casters attempt their checks before you attempt the primary check; no matter their results, the ritual proceeds to the primary check. Secondary checks affect the primary check depending on their results.

[gesalt]

Only the primary needs to succeed, but between the very hard DC and the penalties for failing and crit failing the secondary checks, you effectively need to succeed on every check.