Patti,
It´s a 50% chance. If the father has cf ,he will always pass one cf gene to the child, the other gene (mother´s one) can be a cf gene (then the child will hava cf) or a no cf gene (50% chances), in this last case the child will be a carrier.
Although 3 out of 4 genes are affected by cf, you cannot pass both of the father´s ones together, you will have one gene from each parent that´s why it´s a 50% chance.
Sorry if I didn´t explained this very well, but english is my second language <img src="i/expressions/face-icon-small-smile.gif" border="0">.
By the way could you tell me how many mutations was your husband tested for?. I was tested by ambry (1500 mutations) and they told me the chance of being a carrier and testing negative would be 1/2500. By the way I tested negative!!! So happy!!!
Rita, Boyfriend with cf diagnosed at 35 (last year)