The ratio of men to women in a certain factory is 3:4. There are 204 men. How many workers are there?

Let's assume the number of men in the factory is 3x.

Therefore, the number of women in the factory is 4x.
Given that there are 204 men, 3x = 204.
Dividing both sides of the equation by 3 gives x = 68.
The total number of workers in the factory is the sum of men and women: 204 + 4x = 204 + 4*68 = 204 + 272 = <<204+272=476>>476. Answer: \boxed{476}.