High volumes of wastewater with considerable levels of organic and phenolic compounds and solid material are produced during pistachio processing. There is not a commonly adopted treatment technology for the wastes produced during pistachio processing. The objective of this study is to evaluate the anaerobic digestability and biogas production capacity of pistachio processing wastewater in upflow anaerobic sludge blanket (UASB) reactors for the first time in the literature. The results indicated that pistachio processing wastewater can be treated anaerobically with efficiencies comparable with other high-strength agricural wastewaters. The maximum chemical oxygen demand (COD) removal efficiency and methane yield values obtained were 89.77%+/- 2.4% and 332.5 +/- 104.5 mL CH4 g COD-1, respectively, at an organic loading rate (OLR) of 4.56 +/- 0.87 g L-1 day-1. If the annual pistachio processing wastewater produced in Turkey per year (520,000 m3) is digested anaerobically in a UASB reactor, 13,000 t of COD could be eliminated and 3.9 million cubic meters of methane (28,200 mWh of energy) can be produced.