Helsinki slang is a local variation of the Finnish language mainly used in the capital Helsinki.

Helsinki slang is based on colloquial Finnish (puhekieli, see spoken Finnish) but its characteristic feature is its large amount of slang words, most often with non-Finnish etymologies, replacing common everyday nouns, verbs and adjectives.

Helsinki slang dates back to the early 20th century, before the Winter War, but it only became really popular in the 1950s among young men who wanted to rebel against their parents and impress young women. Today, Helsinki slang has all but lost its "tough guy" image, and thanks to a recent trend of media portrayal in good light and various slang books, it has become something of a cultural phenomenon and research interest.

Although like any local variation, Helsinki slang constantly evolves, most adult speakers of Helsinki slang still consider the 1950s version the "real" slang. By far the most of the slang words right up to the 1980s come from Russian and Swedish. Since the 1990s, because of globalisation and the prominence of the Internet, new slang words have usually come from English, but these are considered neologisms at best and sucking-up to Americans at worst, by adult speakers who grew up with 1950s-style slang.

Helsinkians themselves never refer to their slang as "Helsinki slang" but instead as "stadin slangi". Stadi is a slang word, coming from the Swedish stad (city), so taken literally, the name would mean "slang of the city", but Helsinkians have a steadfast opinion that only Helsinki may be called "stadi", the other cities are referred to by the normal Finnish word for "city", kaupunki. In addition, the only name Helsinkians use to refer to Helsinki itself is stadi. Calling the city by its more obvious colloquial form, Hesa, is taken as sign of non-Helsinkian, even rural, background.

Usage and examples

Slang words in Helsinki slang obey normal Finnish grammar, regardless of their etymology. However, Helsinki slang is always both spoken and written as colloquial Finnish, never as properly grammatical kirjakieli (see spoken Finnish). For example, "can you put that in order?" is "voitsä duunaa ton kondiksee?" in Helsinki slang, where duunaa (to do, to make) and kondis (condition, order, working) are slang words. Trying to write the sentence in "properly grammatical" form, as *"voitko sinä duunata tuon kondikseen?", would be erroneous.

Some literary works in Helsinki slang can contain long sentences with a large density of slang words. Examples include "Hei sporakuski, stikkaa dörtsi posee, tääl on galsa blosis, bonjaatsä?" (meaning "Hey, tram driver, close the door, it's a cold wind in here, you understand?", from the Viivi & Wagner comics) and "Kelaa, snadi jeesaaja, kui iisii täl ois stedaa" (meaning "Think, little helper, how easy it would be to clean with this", from Sami Garam's slang version of Aku Ankka). (Slang words are shown in bold face.)