I haven't seen the actual decision yet, but a Chicago Tribune story suggests that the judge was persuaded that limiting marriage to opposite-sex couples is a form of sex discrimination. That's been a common and usually unsuccessful argument in gay-marriage cases.

There's apparently an immediate route available to the state supreme court, which could handle the case itself or decide to let the intermediate state appellate court consider it first. While the same-sex couples involved are celebrating, my guess is that the decision will be stayed pending appeal. Iowa does not have a state constitutional amendment banning gay marriage, but this is sure to fire up support for one.

If the decision seems to break any new ground, I'll have more to say about it.

UPDATE: If you're having trouble accessing the Tribune story, here's one from the Sioux City Journal.

FURTHER UPDATE: The decision is available here. Thanks to Steve Sanders, who filed an amicus brief in the case, for making the text available.