Narcissism in one parent is not, in itself, grounds for a family court to award custody to the other parent. Laws vary by state, but the general rule, as reported by About.com, is that the parent seeking sole custody bears the burden of proving she is more fit in court.
According to About.com, courts are often reluctant to sever parental rights in custody disputes, as the assumption underlying much of family law is that children are more likely to thrive with both parents in their lives. Measures that interfere with the relationship one parent has with the child are therefore undertaken only when necessary. Usually, this requires that the parent seeking sole custody demonstrate the superiority of such a ruling. Know that the court's only principle in deciding custody is the best interests of the child, not the child's parents, and that the perceived moral failings or personality disorders of a parent are not considered unless they directly impact the well-being of the child.
WebMD notes that unresolved disputes between parents have a negative impact on the growth and development of children. Children as young as 12 months show signs of distress when parents fight, and surprisingly teenagers have proven to be even more sensitive to parental conflict.