It’s an STD. The abbreviation STD is pronounced as separate letters. Since the S starts with a vowel sound ("ess"), it takes the article "an".

It’s an STD. The abbreviation STD (Sexually Transmitted Disease) is pronounced as separate letters. Since the first letter, the S, starts with a vowel sound ("ess"), it takes the article "an".

Do you need an STD test?

Do you need a STD test?

Remember, the rule for choosing between "a" and "an" is based on the initial sound of the word that follows, and not how it's spelled.

You should visit an STD clinic as soon as possible.

Do you know where to get an STD treatment?

And we always say "an S", not "a S".

The abbreviation STD begins with an S.

Follow the same strategy with other abbreviations that start with S and are pronounced as separate letters; for example, we say:

• an SEO (Search Engine Optimization)
• an SLA (Service-Level Agreement)
• an SMS (Short Message Service)
• an SMTP (Simple Mail Transfer Protocol)
• an SSD (Solid-State Drive)
• an SUV (Sport Utility Vehicle)
• an SVG (Scalable Vector Graphics)