Display latest post from category

where?

in what context?

what theme are you using?

http://codex.wordpress.org/Class_Reference/WP_Query

example:

<?php $cat_id = 27; //the certain category ID
$latest_cat_post = new WP_Query( array('posts_per_page' => 1, 'category__in' => array($cat_id));
if( $latest_cat_post->have_posts() ) : while( $latest_cat_post->have_posts() ) : $latest_cat_post->the_post();
//here whatever you need to display; possibly copy parts from loop-single.php//
the_title();
the_content();
//etc.
endwhile; endif; ?>

my mistake – I missed to close a bracket;

try:

<?php $cat_id = 7; //the certain category ID
$latest_cat_post = new WP_Query( array('posts_per_page' => 1, 'category__in' => array($cat_id)));
if( $latest_cat_post->have_posts() ) : while( $latest_cat_post->have_posts() ) : $latest_cat_post->the_post();  ?>

<h1><?php the_title(); ?></h1>	

<?php the_content(); ?>

<?php endwhile; endif; ?>

am using pages not posts, does that matter?

what are you trying to show?

a static page (the latest published page)?
-static pages do not have categories.

or the latest post of a certain category?

but the latest post does not display

do you have a category in your site with the category ID 7 and at least one published post in it?

Sorry if thats confused matters.

not at all – it is just a totally different question.

you can use an adapted query:

<?php if( is_page() ) :
$latest_child_page = new WP_Query( array('posts_per_page' => 1, 'post_type' => 'page', 'post_parent' => $post->ID));
if( $latest_child_page->have_posts() ) : while( $latest_child_page->have_posts() ) : $latest_child_page->the_post();  ?>

<h1><?php the_title(); ?></h1>	

<?php the_content(); ?>

<?php endwhile; endif;
endif; //ends 'if( is_page() )'// ?>

basically, when you are on a static page (any static page), the code will try to get the latest child page of that page.

-alternatively, try work with: http://codex.wordpress.org/Function_Reference/get_pages