<b><i>Purpose:</i></b> Females with in-hospital treatment for acute cystitis (AC) or pyelonephritis may benefit from catheterization at admission. <b><i>Methods:</i></b> All female patients with AC or pyelonephritis requiring in-hospital treatment at University Hospital Frankfurt (2004–2019) were retrospectively analyzed. Logistic regression models were used to predict the catheter value. <b><i>Results:</i></b> Of 310 female patients, 40% harbored AC versus 60% pyelonephritis, of whom 62% and 74% received a catheter at admission: C-reactive protein (CRP) and white blood count (WBC) were significantly elevated in AC and pyelonephritis catheter versus no catheter patients (both <i>p</i> &#x3c; 0.05). Time to CRP and WBC nadir did not differ between the AC catheter versus no catheter group (both <i>p</i> &#x3e; 0.05). Conversely, time to CRP nadir was prolonged in pyelonephritis catheter patients. AC and pyelonephritis catheter patients exhibited a prolonged antibiotic treatment and length of stay (LOS, both <i>p</i> &#x3c; 0.05). In multivariable analyses, CRP &#x3e;5 ng/mL was a predictor for receiving a catheter in all patients. In AC, a positive urine culture and fever predicted, respectively, prolonged LOS or antibiotic treatment (all <i>p</i> &#x3c; 0.05). <b><i>Conclusion:</i></b> Risk factors exist with regard to receiving a catheter and prolonged antibiotic treatment or LOS in females with AC or pyelonephritis. A catheter may not accelerate recovery or WBC nadir.