Background : Despite the recent attention in the literature and the media regarding methamphetamine (MA) abuse, particularly among men who have sex with men (MSM), there still exists a paucity of MA studies among heterosexual populations. From general drug use populations and among MSM, MA has been found to be associated with greater HIV-risk through drug use and sex behaviors. This study aims to contribute key areas of research to the existing literature on heterosexual MA- using populations regarding differences in sociodemographic characteristics, drug use and sex behaviors, and motivations for initiation and current use of MA use by (1) binge MA use, (2) gender, and (3) injection drug use. Methods: Between 2001 and 2005, data were collected on 452 HIV-negative MA users aged 18 and older in San Diego, CA, who had used MA at least twice and had engaged in unprotected sex in the previous 2 months. Separate logistic regression models identified significant factors associated with binge MA use, gender, or injection drug use. Results: Of 452 participants, mean age was 36.6 years; 68% were male; ethnicity was 49.4% Caucasian, 26.8% African-American, and 12.8% Hispanic; 55% were never married; and 58% never attended college. Binge MA use was associated with greater frequency of MA use, ever treated for MA use, injection drug use, higher Beck Depression Inventory (BDI) score, initiating MA "to experiment", and engaging in sex marathons while high on MA. Men were more likely to engage in sex marathons and to use MA "to enhance sexual pleasure," whereas females were younger, and more likely to be married, report a recent sexually transmitted infection (STI) diagnosis, introduced to MA by a sex partner, higher BDI scores, and to use MA "to lose weight." Use of MA by injection was associated with being Caucasian, homeless, more years and quantity of MA use, history of felony conviction, and a recent STI. Conclusions : HIV-negative heterosexual MA users are not a homogeneous group. Differences in gender, route of MA administration and pattern of MA use should be considered in the design and implementation of interventions for decreasing HIV risks associated with MA use.