Nitric oxide has a significant role in the pathogenesis of bronchial asthma and hypertension. Its synthesis is catalyzed by NO synthases. The nucleotide composition of genes coding for these enzymes can affect their activity; therefore, it is important to understand the effect of the NOS3 786C/T polymorphism (rs2070744) on the blood levels of nitric oxide in patients with bronchial asthma and hypertension. Our study recruited 71 individuals. The main group consisted of 24 asthmatic hypertensive patients. Two comparison groups included patients with isolated asthma and isolated hypertension. All patients were genotyped for the NOS3 786C/T polymorphism. We measured total nitric oxide metabolites in their blood using a photocolorimetric technique and the Griess reagent. The levels of nitric oxide in the exhaled air were determined electrochemically using a portable NObreath monitor. The blood levels of nitric oxide metabolites amounted to 69.7 (60.0; 70.4) μmol/l in the CC genotype carriers, 68.9 (57.7; 77.4) μmol/l in the CT genotype carriers and 67.7 (59.7; 79.3) μmol/l in the patients with the TT genotype (p = 0.843). Individually, the groups demonstrated a clear association between the NOS3 786C/T polymorphism and the blood levels of nitric oxide metabolites. The patients with bronchial asthma and hypertension demonstrated a tendency to increasing nitric oxide levels following the pattern CC < CT < TT (p = 0.033 and p = 0.024, respectively). Thus, the C allele of the NOS3 786C/T polymorphism is associated with lower blood levels of nitric oxide metabolites in patients with bronchial asthma and hypertension.