Objective: To evaluate the genetic and environmental relationship among prostatitis and other urological conditions, including benign prostatic hyperplasia (BPH) and prostate cancer (CaP), a classical twin design and biometric modeling was used. While prostatitis – characterized by pain and voiding symptoms, no clear etiology, and functional and quality of life impairments – co-occurs with other urinary conditions, the degree of shared overlapping etiological processes among them remains unclear. We examined the contribution of genetic and environmental factors to these conditions and the etiology of their associations at the level of genetic and environmental influences. Methods: 4380 monozygotic and dizygotic male twin pairs from the Vietnam Era Twin Registry reported lifetime physician-diagnosed prostatitis (combined acute and chronic), bladder problems, enlarged prostate/BPH, and CaP. Multivariate biometrical modeling estimated the magnitude of genetic and environmental influences for each condition, as well as their genetic and environmental covariance. The common pathway model tested the assumption that covariation among these urinary conditions is determined by a single latent factor. Results: Overall prevalence of prostatitis was 2.7%. Heritability estimates ranged from 19% for bladder problems to 42% for CaP. Significant shared environmental influences were present for CaP (12%), enlarged Prostate/BPH (10%) but were smaller than genetic influences. A reduced one factor common pathway model provided the best fit, suggesting that covariation among the conditions is determined by a shared latent factor. Conclusions: We identified a common, genetically-influenced factor that accounts for much of the comorbidity among these four disease conditions. Non-shared environmental factors also make a significant contribution.