Mycoplasma genitalium was first isolated from urethral swab specimens of male patients with non-gonococcal urethritis. However, the isolation of M. genitalium strains from clinical specimens has been difficult. Co-cultivation with Vero cells is one available technique for the isolation of M. genitalium. The strains that can be used for antimicrobial susceptibility testing by broth dilution or agar dilution methods are limited. Macrolides, such as azithromycin (AZM), have the strongest activity against M. genitalium. However, AZM-resistant strains have emerged and spread. Mutations in the 23S rRNA gene contribute to the organism's macrolide resistance, which is similar to the effects of the mutations in macrolide-resistant Mycoplasma pneumoniae. Of the fluoroquinolones, moxifloxacin (MFLX) and sitafloxacin have the strongest activities against M. genitalium, while levofloxacin and ciprofloxacin are not as effective. Some clinical trials on the treatment of M. genitalium-related urethritis are available in the literature. A doxycycline regimen was microbiologically inferior to an AZM regimen. For cases of treatment failure with AZM regimens, MFLX regimens were effective.