Upset may refer to:

• Upset (band), an American rock band
• Upset (competition), where a likely winner loses
• "Upset" (Hit the Floor), an episode of the television series Hit the Floor
• Upset (horse), a racehorse
• Upset (wastewater treatment), temporarily decreased effluent quality
• Aircraft upset, a dangerous aviation condition
• Upper set, in mathematics
• UpSet Plot, in data visualization
• Upset forging, a forging process where a workpiece's diameter is increased by compressing its length.
• Upset, a type of fault in wood, see Shakes (timber) § Thunder shake or upset