Before Slovenia went independent in 1991, Slovenian parents used to adopt children mainly from Yugoslav republic.
As Slovenia left Yugoslavia, it became more difficult to adopt a child from the former Yugoslavia, the Office said as it explained the big rise in adoptions.
It said that half of all adopted children last year (35) came from abroad.
The majority (19) were born in the Russian Federation, while 10 children came from five African countries.
As many as 33 children adopted in 2012 were one year old at the time of the adoption, while only seven were aged 10 or more.
In 19 cases children were adopted by their biological parent's partner.