'Diagnosises' or 'Diagnoses': What is the Plural of 'Diagnosis'? (2025)

When deciding how to make the plural form of the word ‘diagnosis,’ you might not quite know the right way to do it. The pluralization rules can differ from word to word, which can make it hard to remember.

The plural of ‘diagnosis’ is ‘diagnoses.’ It is incorrect to say ‘diagnosises’ or any other variation.

Plural of Diagnosis

The word ‘diagnosis’ doesn’t follow the standard pluralization rules, which is why some people find it difficult to pluralize the word correctly.

So, what are the standard pluralization rules?

Standard Pluralization Rules

When forming the plural version of a noun in the English language, the standard rule is that with most nouns, you simply add an ‘s’ or ‘es.’

Take a look at some examples:

• Road > Roads
• Test > Tests
• Roof > Roofs
• Latch > Latches
• Match > Matches
• Tux > Tuxes

Other words, such as words that end in ‘f’ or ‘fe’ are be treated differently. With words that end in ‘f’ or ‘fe,’ you’d drop those letters and add a ‘ves.’

Let’s take a look at some examples:

• Knife > Knives
• Life > Lives
• Leaf > Leaves
• Calf > Calves
• Wolf > Wolves
• Wife > Wives

What is the Plural of Diagnosis

The plural of diagnosis is ‘diagnoses.’ It follows the same rules that words like [example] follow. Instead of just adding an ‘es,’ you’d change the ‘is’ to an ‘es.’ Check out some examples:

• Analysis > Analyses
• Ellipsis > Ellipses
• Crisis > Crises
• Thesis > Theses
• Axis > Axes

Definition and Meaning

Now that you know how to make plural nouns and how this word is treated differently let’s learn what it means.

Merriam-Webster defines the word as “the art or act of identifying a disease from its signs and symptoms,” “the decision reached by diagnosis,” “investigation or analysis of the cause or nature of a condition, situation, or problem,” and “a statement or conclusion from such an analysis.”

It could also mean “a concise technical description of a taxon” in biology.

Cambridge Dictionary defines it as “a judgment about what a particular illness or problem is, made after examining it.”

How to Use ‘Diagnoses’ and ‘Diagnoses’ in a Sentence

Since we’ve already covered the plural form and definition of the word, let’s talk about how to use it in a sentence.

Here are some examples of how to use the singular form in a sentence:

• Jane got her cancer diagnosis this morning, which crushed her.
• I don’t have a diagnosis yet; we’re not sure what’s wrong yet.
• We got a diagnosis we didn’t agree with, so we got a second opinion.

Here are some examples of how to use the plural form in a sentence:

• She had MS and cancer, two diagnoses in one.
• The doctor’s diagnoses were devastating for Meredith; she didn’t know she had more than one ailment.
• Two diagnoses in one day is a lot for one person.

Singular and Plural Possessive Forms

The singular possessive form of the word ‘diagnosis’ is ‘diagnosis’s.’ The plural possessive form of the word is ‘diagnoses.’

Here are examples of how to use the singular possessive form in a sentence:

• The diagnosis’s impact on her was more than anyone could’ve imagined.
• The diagnosis’s seriousness was apparent in her tone as soon as she began speaking.
• The diagnosis’s crippling effect on her mental status was undeniable.

Here are examples of how to use the plural possessive form in a sentence:

• The diagnoses’ impact on her gave her a mental breakdown; she has cancer and MS.
• The diagnoses’ effect on her mood was immediate; she understandably went crazy.
• The diagnoses’ was unbelievable; who would’ve thought she’d have cancer and MS?

Concluding Thoughts on ‘Diagnosis’ and ‘Diagnoses’

Remembering how to pluralize words can be tricky, especially for someone who’s just learning the language.

The trick to pluralizing ‘diagnosis’ correctly is to remember that it follows the same rules as words like analysis and axis, in that the ‘is’ is changed to an ‘es.’

Check out our library of confusing words if you have trouble remembering how to pluralize or spell words.