standard errors

[Sevila Sev]

Is Stata's default robust SE:

 ,robust or ,vce(robust)

heteroskedasticity-robust standard errors?

[Fei Wang]

Yes, it is.

[Carlo Lazzaro]

Sevilla:
if you refer to -xtreg- (instead of -regress-), please note that both -robust- and -vce(cluster clusterid)- options do the very same job (i.e., they take both heteroskedastcity and/or autocorrelation into account).