PURPOSE: To describe the unique clinical features of phlyctenular keratitis, including the association with meibomitis, in young patients. DESIGN: Observational case series. METHODS: The study population consisted of 23 Japanese patients aged under 35 years with phlyctenular keratitis. We examined their clinical history, signs and symptoms, human leukocyte antigen (HLA), bacterial cultures of meibum, and the efficacy of antibiotics. The minimal diagnostic criteria included corneal nodules consisting of cellular infiltrates and superficial neovascularization. RESULTS: Of the 23 patients, 20 (87% )- were women, and 13 (56.5% ) had a history of chalazia. In all cases, the lesions and the severity of corneal nodules and neovascularization corresponded well with the location and the severity of meibomitis. The frequency of HLA- A26 and HLA- B35 was significantly increased in our patients (P=.003 and .016, respectively). Propionibacterium acnes in bacterial cultures of pure meibum in 12 of the 20 patients (60% ) was statistically more highly positive than those in four of the 17 age-matched normal control subjects (23.5% ; P=.028). CONCLUSION: The characteristics of phlyctenular keratitis in our cases include significantly higher prevalence in female patients, severity variation of ocular surface manifestation corresponding to meibomitis, specific HLA association, and possible P. acnes involvement. PURPOSE: To describe the unique clinical features of phlyctenular keratitis, including the association with meibomitis, in young patients. DESIGN: Observational case series. METHODS: The study population consisted of 23 Japanese patients aged under 35 years with phlyctenular keratitis. We examined their clinical history of signs and symptoms, human leukocyte antigen (HLA), bacterial cultures of meibum, and the efficacy of antibiotics. The minimal diagnostic criteria included corneal nodules consisting of cellular infiltrates and superficial neovascularization. RESULTS: Of the 23 patients, 20 (87% ) - were women, and 13 (56.5%) had a history of chalazia. In all cases, the lesions and the severity of corneal nodules and neovascularization corresponded well with the location and the severity of meibomitis. The frequency of HLA- A26 and HLA - B35 was significantly increased in our patients (P = .003 and .016, respectively). Propionibacterium acnes in bacterial cultures of pure meibum in 12 of t The 20 patients (60%) were statistically significantly more highly positive than those in four of the 17 age-matched normal control subjects (23.5%; P = .028). CONCLUSION: The characteristics of phlyctenular keratitis in our cases include significantly higher prevalence in female patients, severity variation of ocular surface manifestation corresponding to meibomitis, specific HLA association, and possible P. acnes involvement.