BACKGROUND: Preeclampsia (PE) is more common at high than low altitude and contributes to the altitude-related decline in birth weight. Since inflammatory markers are implicated in PE, we asked if such markers differed in PE vs. normotensive pregnant (NORM) women residing at high altitude (3600-4100 m), and were related to uterine artery blood flow (UA BF) or fetal growth. METHODS: Subjects were 33 Andean pregnant residents of Bolivia, comprising six with early-onset PE (≤ 34 wk), 12 with late-onset PE (> 34 wk), and 15 gestational-age matched NORM. Maternal pro- and anti-inflammatory cytokines were measured using a multiplex bead-based assay and UA BF by Doppler ultrasound. RESULTS: PE compared to NORM women had higher levels of the pro-inflammatory cytokines IL-6 and IL-8 as well as higher levels of the anti-inflammatory cytokine IL-1ra, but only IL-6 levels were higher when gestational age was controlled. Women with early- vs. late-onset PE had higher TNFα levels, and higher IL-6 was negatively correlated with birth weight in all women at ≤ 34 wk. We suggest that pro-inflammatory factors influence both the timing and severity of PE at high altitude.