To investigate the incidence, bacteriologic features, and risk factors of posttranssphenoidal surgery (post-TSS) meningitis and/or bacteremia.This retrospective study included 3242 patients who underwent TSS for pituitary adenoma at the Department of Neurosurgery of Peking Union Medical College Hospital between January 2012 and December 2016. Clinical data for patients with and without post-TSS meningitis and/or bacteremia were compared and analyzed.Meningitis and bacteremia developed after 27 (0.8%) and 26 (0.8%) procedures, respectively, and 6 patients (0.2%) developed both. Gram-positive organisms (coagulase-negative staphylococci, Streptococcus pneumonia, and S viridans) predominated in meningitis, whereas gram-negative organisms (Klebsiella pneumonia, Enterobacter aerogenes, and Escherichia coli) predominated in bacteremia. All identified species were sensitive to amikacin, imipenem, and meropenem. Antibiotic treatment cured 52 patients (7 died). In a multivariate analysis, the risk of meningitis and/or bacteremia was independently associated with diabetes (P < 0.001; odds ratio [OR], 6.06), previous surgery at the same location (P < 0.001; OR, 4.23), intraoperative cerebrospinal fluid leakage (P < 0.001l; OR, 4.63), and an endoscopic approach (P = 0.001; OR, 2.50).Meningitis and/or bacteremia remain critical postoperative complications of TSS for pituitary adenoma. The pathogens with drug sensitivity to antibiotics differed between meningitis and bacteremia. Early blood and cerebrospinal fluid bacterial cultures, drug susceptibility analyses, and appropriate antibiotic treatment can help control the rate of infection.