Purpose To compare complete blood count (CBC) parameters and neutrophil/lymphocyte ratio (NLR) between patients with infectious uveitis (IU) and those with non-infectious uveitis (NIU) during the first acute uveitis attack (AUA). Methods The records of 119 patients admitted with the first AUA between 2016 and 2019 and whose diagnosis was unknown at the time of admission were retrospectively reviewed. The patients were divided into two groups, IU and NIU according to diagnoses after ocular and systemic workup. The IU group was also divided into subgroups as uveitis associated with local ocular infections and systemic infections. The complete blood count and associated indices of patients calculated from samples taken during the attack were compared between the groups. Results A total of 60 NIU cases (mean age: 43.5 +/- 11.6 years) and 59 IU cases (43.3 +/- 14.7 years) were examined. Twenty-six of the NIU cases were female and 34 were male, while 32 of the IU cases were female and 27 were male. The localization of uveitis was similar in the IU and NIU groups (anterior: 11 vs. 18, intermediate: 3 vs. 6, posterior: 28 vs. 14, panuveitis: 17 vs. 22). The NLR values were significantly increased in patients with IU compared to those with NIU (p = 0.047). When the NLR is compared between NIU and subgroups of IU, this value was only found significantly increased in uveitis due to a systemic infection (n = 12) (p < 0.001). The mean white blood cell (WBC) count (p < 0.001) and neutrophil values (p < 0.001) were also observed significantly higher in the uveitis associated with systemic infectious diseases when compared with uveitis associated with local ocular infections and NIU group. Conclusion In the current study, NLR values are compared with autoimmune uveitis and systemic infectious uveitis for the first time in patients with AUA. This ratio has been found significantly higher in uveitis associated with systemic infections. The use of CBC parameters and indices, especially the NLR, may be instrumental in assessing patients presenting with first AUA, particularly when there is no clear explanation or underlying cause.