What is Incest? A relationship is incestuous if people related by blood or adoption are in an intimate, sexual relationship. Is it a Crime? Yes, it is. In the United States, incestuous relations are generally considered a crime that is punishable by law. Incestuous marriages are illegal in all the states of the United States. Despite this, not all states have laws against incestuous relationships and these incestuous relationships may continue to take place. Texas Laws on Incest In Texas, incestuous relation is a crime. In fact, it is an act of prohibited sexual conduct. It must involve the penetration of the male sex organ into the mouth, vagina, or anus. The degree of the penalty imposed depends on the kind of sexual conduct that has taken place. Incestuous Marriages Incestuous marriages are also illegal and prohibited. Should it ever happen that there was an incestuous marriage, this marriage can be annulled. Marriage is illegal if the spouses are first cousins or closer. That means sexual relationship or marriage is not allowed between parents and their children, between the children, between children and their uncles or aunts, between first cousins, and those others that may be prohibited by law. However, if for some reason first cousins were able to get married, their marriage is not considered void. Texas will recognize its validity. Other states may allow for incestuous relationships but prohibit incestuous marriages. Texas deems any kind of incestuous relationship illegal. Incestuous relations, especially those that involve sexual conduct of any sort, are illegal and punishable by law in the state of Texas.