Historically, crime groups rarely included women, but debates continue over whether women today are more violent, or have greater involvement in mixed-sex or all-female crime partnerships. We analyze variability in sex stratification of violent crime groups over time, and across situational offense characteristics, utilizing co-offending data from Supplementary Homicide Reports (SHR; 1980-2007) for homicide and National Incident-Based Reporting System (NIBRS; 1995-2007) for robbery, felony, and simple assault. Descriptive and multivariate results show crime groups remain highly sex-stratified and male-dominated, particularly when the offense is serious, instrumental, and involves strangers and/or access to weapons. Opposite-sex partners are more likely for expressive violence victimizing family/intimates.