We are planning a week long trip to Portugal this spring. How long should we plan to be in Lisbon? Where else should we be sure to visit? (We are active and like to bike, hike, etc.)

I would look at 4 to 5 days in Lisbon iyself.

Lucky You...Portugal is fantastic!
I would visit Coimbra...beautiful town with one of the oldest universities in Europe...lovely to walk around!
Also...definately Porto...lots to do and fantastic city.
I have not been but understand Duoro valley is lovely...this is wine country where I,m sure you could get some biking in!
Hope this helps

What we did was 3 nights in Lisbon, 2 in Evora, and 2 in Sesimbra. If you enjoy biking, there is a flat, hard gravel bike trail that winds thru the countryside starting in Evora.
There are lots of pre-historic ruins just outside Evora, and the hill towns on the Spanish border just east of Evora are beutiful. Sesimbra is a scenic little fishing village/resort town about 90 minutes south of Lisbon, with a great stretch of beach.

I'm also planning about 10 days in Lisbon and environs this April, with a trip up to Porto (probably). Unfortunately I am stymied in my planning at the moment, since the conference my husband is attending have stalled in giving us info about flight arrangements. So I will watch this thread, when we get the go-ahead.

I enjoyed a variety of experiences in Portugal -- in Lisbon, Porto, Guimaraes, Braga and Coimbra -- but if you don't enjoy urban sightseeing, and if you don't view travel as trying to "do" someplace in X days, then you might not want to spend much time in Lisbon or Porto (which are two marvelous cities to me).

If you haven't already, read up more on Portugal and the areas that are good for hiking and biking (the cities aren't good for either), and read up on the cities and decide what attractions you want to see there.

There are probably next to ZERO tourists who go to Lisbon and explore the city as a whole, which is rather sprawling. Instead, they go to selected target sights, and never see the rest of the city. If you read up on the most popular sights of Lisbon, you can decide for yourself how long you need to be there to see what interest you.

I'm curious about your reply to the OP with respect to Lisbon. We do like cities, and have been to Portugal previously (Port and the north), but have only spent a morning in Lisbon. I'm thinking that a week in Lisbon is about right, but that up to ten days would be fine too, given a couple of day trips. We do like exploring a place as thoroughly as we can.