Hi Peter, In the traditional sense sister in Law (and son in Law etc) is as it is today.......but I have had children from the wifes first marriage listed in census data as son in law to the head of the household.....etc So in this case they may be half sister and brother........Might pay to check whether one of the parents was married twice, somewhere along the line. Cheers pam from Adelaide Australia Hi List Can someone remind me what the relationship is which would allow a 39 year old Male to call a 13 year old Female his "Sister in Law"? I am puzzled because, as far as I can see, neither the 39 year old nor his Wife seem to be related to the 13 year old in any way Thanks Peter Jones