Slovak preserves the Common Slavic contrast between short and long vowels (referring to the length of the vowel's sound), with the long vowels represented in writing by an acute accent mark. Slovak also has developed a set of diphthongs (ia, ie, iu, ou, and uo) that function as long vowels. The sounds r and l function as either consonants or vowels; as vowels, they can be either long or short. Slovak shares with the Czech language the spelling of the consonants c', š, and z', pronounced [ch], [sh], and [zh], respectively. The Slovak language has gained the soft dental consonants t', d', l', and ñ, but it lacks a soft r existing also in Polish.

Compared with Czech, Slovak word structure has been simplified. Stress falls on the first syllable of a word. Slovak nouns have one of three genders (masculine, feminine, neuter) and six cases (nominative, genitive, dative, accusative, instrumental, locative). The vocative case has been virtually lost. Adjectives agree with nouns in gender, number (singular and plural), and case. Verbs have two tenses (past and present) and two aspects (perfective and imperfective), the latter indicating the duration of the verb's activity. Many verbs have an iterative form, which expresses repeated action. Slovak has a complex numeral system and a well-developed system of indefinite pronouns and adverbs. Slovak word order generally places the most informative elements at the end of a sentence, often violating the language's basic subject-verb-object sentence structure.