"Error in predict.coxph(f.ph.eha, newdata = mort, type = "lp") : Data is not the same size as it was in the original fit" This error message was added in a recent update to predict.coxph. If it needs to reconstruct some aspects from the original fit, such as the X matrix or strata vector, it makes sure that the data set is the same size. It was to stop fit <- coxph(Surv(...... , data=mydata) read in a new copy of mydata predict(fit) then gives wrong results One solution is to use model=TRUE in the orignal coxph call, so that no reconstruction is needed. The lm() function made model=TRUE the default at some point for this very reason, the original lm had model=FALSE to save space. Whether coxph should make the same change is open to debate. Terry Therneau