Aim: Neopterin is a marker associated with cell-mediated immunity produced by interferon-Ɣ-stimulated macrophages. The levels of neopterin in body fluids are elevated in infections, autoimmune diseases, malignancies, and allograft rejections. Recently, it was shown to be associated with the initiation and progression of periodontal disease. This investigation was designed to explore the use of salivary neopterin in predicting the outcome of nonsurgical periodontal therapy (NSPT) in aggressive and chronic periodontitis patients. Materials and Methods: This case-control study with stratified sampling comprised 45 subjects divided into three groups: a control group of 15 periodontally healthy participants, a test Group A of 15 participants with chronic periodontitis, and a test Group B of 15 participants with aggressive periodontitis. Periodontal parameters, including plaque index (PI), gingival index (GI), probing depth (PD), and clinical attachment level (CAL), were recorded at baseline and three months after scaling and root planing (SRP). An enzyme-linked immunosorbent assay (ELISA) analysis was performed to measure neopterin levels in saliva in study groups before and after SRP. Kruskal–Wallis analysis of variance and Mann–Whitney U tests were done for intra- and intergroup comparisons. The correlation between salivary neopterin levels with clinical parameters was done by Karl Pearson’s correlation coefficient. Results: Baseline salivary neopterin levels were least in the control group (5 62 nmol/L), higher in test Group A (9.30 nmol/L), and highest in test Group B (9.76 nmol/L). Three months after SRP, there was a significant reduction in all the clinical parameters, and the reduction in mean salivary neopterin levels were 2.79 and 2.57 in test Group A and test Group B, respectively; the difference was not statistically significant. Conclusion: Salivary neopterin levels have the potential to be utilized as a diagnostic tool for detecting the presence, activity of the disease, and the course of the lesions. It cannot, however, be utilized to distinguish between chronic and aggressive periodontitis.