R.B.
My sister had the same problem with her 18 month old. They started letting him sleep in their bed just so they could get some sleep after numerous attempts of letting him cry it out. She ended up seeing a sleep theripst it got so bad. Here's what she had to do: She had to put a twin bed on the floor in his room. The first week she slept with him on the twin bed in his room---not ideal, I know. The second week her husband had to sleep in the twin bed while the baby was in his crib. When he would cry, all he said was "it is time to sleep Jack, go to sleep. Do not pick them up out of their crib. My sister never thought this would work but talked to a friend that had to do the same thing and it was working for her so my sister tried it after a month of putting it off. After the two week stint he sleeps in his bed through the night, she couldn't believe it. It has now been about a month and he is still in his own bed sleeping throught the night. I'm sure there are different fixes for each case but this worked for her. If it doesn't work I would talk to the Doctor about a pediatric sleep theripst to see what works best for your case. I know it sounds like a lot of work---hope this helps.