The epidemiology of seminal plasma hypersensitivity (SPH) is unknown. Case reports and a previous survey have identified two distinct phenotypes: localized and systemic reactors. The objective of this study was to use an Internet-based questionnaire to characterize and examine the differences among a population of women with suspected SPH. A questionnaire designed to distinguish women with probable SPH was made available via the Internet. Systemic symptoms included generalized pruritus, urticaria, angioedema, wheezing, chest tightness, shortness of breath, dizziness, and loss of consciousness whereas localized symptoms included vaginal burning, pain, swelling, erythema, or blister formation. Respondents with localized or systemic symptoms and whose symptoms were prevented with the use of a condom were included in the analysis. Frequency and means were calculated and further analyzed using chi-square and t-test analyses. A total of 165 women with probable SPH, 79 with systemic symptoms and 86 with only localized symptoms, were included in the analysis. Systemic compared with localized respondents were significantly older (mean age, 29.2 years versus 26.4 years; p = 0.01), had longer duration of symptoms (mean, 58 months versus 40.8 months; p = 0.03), and more frequently reported a family history of atopy (65.8% versus 50%; p < 0.05). Interestingly, significantly more systemic compared with localized respondents reported dog sensitization (11.4% versus 2.3%; p = 0.02). Localized and systemic SPH are more common than previously realized and should be considered in the differential diagnosis of anaphylaxis, vulvovaginitis, and dyspareunia. Additional research investigating the epidemiology, immunopathogenesis, and treatment of this disorder is warranted.