A foster parent is facing charges after allegations he sexually assaulted a youth who was once in his care.

Rodney James Marcynuik, 39, of Airdrie was arrested by Calgary police on Monday.

It's alleged the offences happened between June 2003 and November 2008 in both Calgary and Airdrie.

Police said 18 foster children — all boys — have lived with Marcynuik and his wife between 2001 and 2010.

Marcynuik is charged with one count each of sexual assault, sexual interference, invitation to sexual touching and sexual exploitation by a person in trust or authority.

Investigators haven't yet spoken to the other boys who lived in the home but say the investigation is ongoing.